source: src/linux/universal/linux-4.4/kernel/trace/ring_buffer.c @ 31859

Last change on this file since 31859 was 31859, checked in by brainslayer, 11 days ago

kernel update

File size: 130.3 KB
Line 
1/*
2 * Generic ring buffer
3 *
4 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
5 */
6#include <linux/trace_events.h>
7#include <linux/ring_buffer.h>
8#include <linux/trace_clock.h>
9#include <linux/trace_seq.h>
10#include <linux/spinlock.h>
11#include <linux/irq_work.h>
12#include <linux/uaccess.h>
13#include <linux/hardirq.h>
14#include <linux/kthread.h>      /* for self test */
15#include <linux/kmemcheck.h>
16#include <linux/module.h>
17#include <linux/percpu.h>
18#include <linux/mutex.h>
19#include <linux/delay.h>
20#include <linux/slab.h>
21#include <linux/init.h>
22#include <linux/hash.h>
23#include <linux/list.h>
24#include <linux/cpu.h>
25
26#include <asm/local.h>
27
28static void update_pages_handler(struct work_struct *work);
29
30/*
31 * The ring buffer header is special. We must manually up keep it.
32 */
33int ring_buffer_print_entry_header(struct trace_seq *s)
34{
35        trace_seq_puts(s, "# compressed entry header\n");
36        trace_seq_puts(s, "\ttype_len    :    5 bits\n");
37        trace_seq_puts(s, "\ttime_delta  :   27 bits\n");
38        trace_seq_puts(s, "\tarray       :   32 bits\n");
39        trace_seq_putc(s, '\n');
40        trace_seq_printf(s, "\tpadding     : type == %d\n",
41                         RINGBUF_TYPE_PADDING);
42        trace_seq_printf(s, "\ttime_extend : type == %d\n",
43                         RINGBUF_TYPE_TIME_EXTEND);
44        trace_seq_printf(s, "\tdata max type_len  == %d\n",
45                         RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
46
47        return !trace_seq_has_overflowed(s);
48}
49
50/*
51 * The ring buffer is made up of a list of pages. A separate list of pages is
52 * allocated for each CPU. A writer may only write to a buffer that is
53 * associated with the CPU it is currently executing on.  A reader may read
54 * from any per cpu buffer.
55 *
56 * The reader is special. For each per cpu buffer, the reader has its own
57 * reader page. When a reader has read the entire reader page, this reader
58 * page is swapped with another page in the ring buffer.
59 *
60 * Now, as long as the writer is off the reader page, the reader can do what
61 * ever it wants with that page. The writer will never write to that page
62 * again (as long as it is out of the ring buffer).
63 *
64 * Here's some silly ASCII art.
65 *
66 *   +------+
67 *   |reader|          RING BUFFER
68 *   |page  |
69 *   +------+        +---+   +---+   +---+
70 *                   |   |-->|   |-->|   |
71 *                   +---+   +---+   +---+
72 *                     ^               |
73 *                     |               |
74 *                     +---------------+
75 *
76 *
77 *   +------+
78 *   |reader|          RING BUFFER
79 *   |page  |------------------v
80 *   +------+        +---+   +---+   +---+
81 *                   |   |-->|   |-->|   |
82 *                   +---+   +---+   +---+
83 *                     ^               |
84 *                     |               |
85 *                     +---------------+
86 *
87 *
88 *   +------+
89 *   |reader|          RING BUFFER
90 *   |page  |------------------v
91 *   +------+        +---+   +---+   +---+
92 *      ^            |   |-->|   |-->|   |
93 *      |            +---+   +---+   +---+
94 *      |                              |
95 *      |                              |
96 *      +------------------------------+
97 *
98 *
99 *   +------+
100 *   |buffer|          RING BUFFER
101 *   |page  |------------------v
102 *   +------+        +---+   +---+   +---+
103 *      ^            |   |   |   |-->|   |
104 *      |   New      +---+   +---+   +---+
105 *      |  Reader------^               |
106 *      |   page                       |
107 *      +------------------------------+
108 *
109 *
110 * After we make this swap, the reader can hand this page off to the splice
111 * code and be done with it. It can even allocate a new page if it needs to
112 * and swap that into the ring buffer.
113 *
114 * We will be using cmpxchg soon to make all this lockless.
115 *
116 */
117
118/* Used for individual buffers (after the counter) */
119#define RB_BUFFER_OFF           (1 << 20)
120
121#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
122
123#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
124#define RB_ALIGNMENT            4U
125#define RB_MAX_SMALL_DATA       (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
126#define RB_EVNT_MIN_SIZE        8U      /* two 32bit words */
127
128#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
129# define RB_FORCE_8BYTE_ALIGNMENT       0
130# define RB_ARCH_ALIGNMENT              RB_ALIGNMENT
131#else
132# define RB_FORCE_8BYTE_ALIGNMENT       1
133# define RB_ARCH_ALIGNMENT              8U
134#endif
135
136#define RB_ALIGN_DATA           __aligned(RB_ARCH_ALIGNMENT)
137
138/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
139#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
140
141enum {
142        RB_LEN_TIME_EXTEND = 8,
143        RB_LEN_TIME_STAMP = 16,
144};
145
146#define skip_time_extend(event) \
147        ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
148
149static inline int rb_null_event(struct ring_buffer_event *event)
150{
151        return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
152}
153
154static void rb_event_set_padding(struct ring_buffer_event *event)
155{
156        /* padding has a NULL time_delta */
157        event->type_len = RINGBUF_TYPE_PADDING;
158        event->time_delta = 0;
159}
160
161static unsigned
162rb_event_data_length(struct ring_buffer_event *event)
163{
164        unsigned length;
165
166        if (event->type_len)
167                length = event->type_len * RB_ALIGNMENT;
168        else
169                length = event->array[0];
170        return length + RB_EVNT_HDR_SIZE;
171}
172
173/*
174 * Return the length of the given event. Will return
175 * the length of the time extend if the event is a
176 * time extend.
177 */
178static inline unsigned
179rb_event_length(struct ring_buffer_event *event)
180{
181        switch (event->type_len) {
182        case RINGBUF_TYPE_PADDING:
183                if (rb_null_event(event))
184                        /* undefined */
185                        return -1;
186                return  event->array[0] + RB_EVNT_HDR_SIZE;
187
188        case RINGBUF_TYPE_TIME_EXTEND:
189                return RB_LEN_TIME_EXTEND;
190
191        case RINGBUF_TYPE_TIME_STAMP:
192                return RB_LEN_TIME_STAMP;
193
194        case RINGBUF_TYPE_DATA:
195                return rb_event_data_length(event);
196        default:
197                BUG();
198        }
199        /* not hit */
200        return 0;
201}
202
203/*
204 * Return total length of time extend and data,
205 *   or just the event length for all other events.
206 */
207static inline unsigned
208rb_event_ts_length(struct ring_buffer_event *event)
209{
210        unsigned len = 0;
211
212        if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
213                /* time extends include the data event after it */
214                len = RB_LEN_TIME_EXTEND;
215                event = skip_time_extend(event);
216        }
217        return len + rb_event_length(event);
218}
219
220/**
221 * ring_buffer_event_length - return the length of the event
222 * @event: the event to get the length of
223 *
224 * Returns the size of the data load of a data event.
225 * If the event is something other than a data event, it
226 * returns the size of the event itself. With the exception
227 * of a TIME EXTEND, where it still returns the size of the
228 * data load of the data event after it.
229 */
230unsigned ring_buffer_event_length(struct ring_buffer_event *event)
231{
232        unsigned length;
233
234        if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
235                event = skip_time_extend(event);
236
237        length = rb_event_length(event);
238        if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
239                return length;
240        length -= RB_EVNT_HDR_SIZE;
241        if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
242                length -= sizeof(event->array[0]);
243        return length;
244}
245EXPORT_SYMBOL_GPL(ring_buffer_event_length);
246
247/* inline for ring buffer fast paths */
248static void *
249rb_event_data(struct ring_buffer_event *event)
250{
251        if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
252                event = skip_time_extend(event);
253        BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
254        /* If length is in len field, then array[0] has the data */
255        if (event->type_len)
256                return (void *)&event->array[0];
257        /* Otherwise length is in array[0] and array[1] has the data */
258        return (void *)&event->array[1];
259}
260
261/**
262 * ring_buffer_event_data - return the data of the event
263 * @event: the event to get the data from
264 */
265void *ring_buffer_event_data(struct ring_buffer_event *event)
266{
267        return rb_event_data(event);
268}
269EXPORT_SYMBOL_GPL(ring_buffer_event_data);
270
271#define for_each_buffer_cpu(buffer, cpu)                \
272        for_each_cpu(cpu, buffer->cpumask)
273
274#define TS_SHIFT        27
275#define TS_MASK         ((1ULL << TS_SHIFT) - 1)
276#define TS_DELTA_TEST   (~TS_MASK)
277
278/* Flag when events were overwritten */
279#define RB_MISSED_EVENTS        (1 << 31)
280/* Missed count stored at end */
281#define RB_MISSED_STORED        (1 << 30)
282
283struct buffer_data_page {
284        u64              time_stamp;    /* page time stamp */
285        local_t          commit;        /* write committed index */
286        unsigned char    data[] RB_ALIGN_DATA;  /* data of buffer page */
287};
288
289/*
290 * Note, the buffer_page list must be first. The buffer pages
291 * are allocated in cache lines, which means that each buffer
292 * page will be at the beginning of a cache line, and thus
293 * the least significant bits will be zero. We use this to
294 * add flags in the list struct pointers, to make the ring buffer
295 * lockless.
296 */
297struct buffer_page {
298        struct list_head list;          /* list of buffer pages */
299        local_t          write;         /* index for next write */
300        unsigned         read;          /* index for next read */
301        local_t          entries;       /* entries on this page */
302        unsigned long    real_end;      /* real end of data */
303        struct buffer_data_page *page;  /* Actual data page */
304};
305
306/*
307 * The buffer page counters, write and entries, must be reset
308 * atomically when crossing page boundaries. To synchronize this
309 * update, two counters are inserted into the number. One is
310 * the actual counter for the write position or count on the page.
311 *
312 * The other is a counter of updaters. Before an update happens
313 * the update partition of the counter is incremented. This will
314 * allow the updater to update the counter atomically.
315 *
316 * The counter is 20 bits, and the state data is 12.
317 */
318#define RB_WRITE_MASK           0xfffff
319#define RB_WRITE_INTCNT         (1 << 20)
320
321static void rb_init_page(struct buffer_data_page *bpage)
322{
323        local_set(&bpage->commit, 0);
324}
325
326/**
327 * ring_buffer_page_len - the size of data on the page.
328 * @page: The page to read
329 *
330 * Returns the amount of data on the page, including buffer page header.
331 */
332size_t ring_buffer_page_len(void *page)
333{
334        return local_read(&((struct buffer_data_page *)page)->commit)
335                + BUF_PAGE_HDR_SIZE;
336}
337
338/*
339 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
340 * this issue out.
341 */
342static void free_buffer_page(struct buffer_page *bpage)
343{
344        free_page((unsigned long)bpage->page);
345        kfree(bpage);
346}
347
348/*
349 * We need to fit the time_stamp delta into 27 bits.
350 */
351static inline int test_time_stamp(u64 delta)
352{
353        if (delta & TS_DELTA_TEST)
354                return 1;
355        return 0;
356}
357
358#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
359
360/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
361#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
362
363int ring_buffer_print_page_header(struct trace_seq *s)
364{
365        struct buffer_data_page field;
366
367        trace_seq_printf(s, "\tfield: u64 timestamp;\t"
368                         "offset:0;\tsize:%u;\tsigned:%u;\n",
369                         (unsigned int)sizeof(field.time_stamp),
370                         (unsigned int)is_signed_type(u64));
371
372        trace_seq_printf(s, "\tfield: local_t commit;\t"
373                         "offset:%u;\tsize:%u;\tsigned:%u;\n",
374                         (unsigned int)offsetof(typeof(field), commit),
375                         (unsigned int)sizeof(field.commit),
376                         (unsigned int)is_signed_type(long));
377
378        trace_seq_printf(s, "\tfield: int overwrite;\t"
379                         "offset:%u;\tsize:%u;\tsigned:%u;\n",
380                         (unsigned int)offsetof(typeof(field), commit),
381                         1,
382                         (unsigned int)is_signed_type(long));
383
384        trace_seq_printf(s, "\tfield: char data;\t"
385                         "offset:%u;\tsize:%u;\tsigned:%u;\n",
386                         (unsigned int)offsetof(typeof(field), data),
387                         (unsigned int)BUF_PAGE_SIZE,
388                         (unsigned int)is_signed_type(char));
389
390        return !trace_seq_has_overflowed(s);
391}
392
393struct rb_irq_work {
394        struct irq_work                 work;
395        wait_queue_head_t               waiters;
396        wait_queue_head_t               full_waiters;
397        bool                            waiters_pending;
398        bool                            full_waiters_pending;
399        bool                            wakeup_full;
400};
401
402/*
403 * Structure to hold event state and handle nested events.
404 */
405struct rb_event_info {
406        u64                     ts;
407        u64                     delta;
408        unsigned long           length;
409        struct buffer_page      *tail_page;
410        int                     add_timestamp;
411};
412
413/*
414 * Used for which event context the event is in.
415 *  NMI     = 0
416 *  IRQ     = 1
417 *  SOFTIRQ = 2
418 *  NORMAL  = 3
419 *
420 * See trace_recursive_lock() comment below for more details.
421 */
422enum {
423        RB_CTX_NMI,
424        RB_CTX_IRQ,
425        RB_CTX_SOFTIRQ,
426        RB_CTX_NORMAL,
427        RB_CTX_MAX
428};
429
430/*
431 * head_page == tail_page && head == tail then buffer is empty.
432 */
433struct ring_buffer_per_cpu {
434        int                             cpu;
435        atomic_t                        record_disabled;
436        struct ring_buffer              *buffer;
437        raw_spinlock_t                  reader_lock;    /* serialize readers */
438        arch_spinlock_t                 lock;
439        struct lock_class_key           lock_key;
440        unsigned long                   nr_pages;
441        unsigned int                    current_context;
442        struct list_head                *pages;
443        struct buffer_page              *head_page;     /* read from head */
444        struct buffer_page              *tail_page;     /* write to tail */
445        struct buffer_page              *commit_page;   /* committed pages */
446        struct buffer_page              *reader_page;
447        unsigned long                   lost_events;
448        unsigned long                   last_overrun;
449        local_t                         entries_bytes;
450        local_t                         entries;
451        local_t                         overrun;
452        local_t                         commit_overrun;
453        local_t                         dropped_events;
454        local_t                         committing;
455        local_t                         commits;
456        unsigned long                   read;
457        unsigned long                   read_bytes;
458        u64                             write_stamp;
459        u64                             read_stamp;
460        /* ring buffer pages to update, > 0 to add, < 0 to remove */
461        long                            nr_pages_to_update;
462        struct list_head                new_pages; /* new pages to add */
463        struct work_struct              update_pages_work;
464        struct completion               update_done;
465
466        struct rb_irq_work              irq_work;
467};
468
469struct ring_buffer {
470        unsigned                        flags;
471        int                             cpus;
472        atomic_t                        record_disabled;
473        atomic_t                        resize_disabled;
474        cpumask_var_t                   cpumask;
475
476        struct lock_class_key           *reader_lock_key;
477
478        struct mutex                    mutex;
479
480        struct ring_buffer_per_cpu      **buffers;
481
482#ifdef CONFIG_HOTPLUG_CPU
483        struct notifier_block           cpu_notify;
484#endif
485        u64                             (*clock)(void);
486
487        struct rb_irq_work              irq_work;
488};
489
490struct ring_buffer_iter {
491        struct ring_buffer_per_cpu      *cpu_buffer;
492        unsigned long                   head;
493        struct buffer_page              *head_page;
494        struct buffer_page              *cache_reader_page;
495        unsigned long                   cache_read;
496        u64                             read_stamp;
497};
498
499/*
500 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
501 *
502 * Schedules a delayed work to wake up any task that is blocked on the
503 * ring buffer waiters queue.
504 */
505static void rb_wake_up_waiters(struct irq_work *work)
506{
507        struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
508
509        wake_up_all(&rbwork->waiters);
510        if (rbwork->wakeup_full) {
511                rbwork->wakeup_full = false;
512                wake_up_all(&rbwork->full_waiters);
513        }
514}
515
516/**
517 * ring_buffer_wait - wait for input to the ring buffer
518 * @buffer: buffer to wait on
519 * @cpu: the cpu buffer to wait on
520 * @full: wait until a full page is available, if @cpu != RING_BUFFER_ALL_CPUS
521 *
522 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
523 * as data is added to any of the @buffer's cpu buffers. Otherwise
524 * it will wait for data to be added to a specific cpu buffer.
525 */
526int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full)
527{
528        struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer);
529        DEFINE_WAIT(wait);
530        struct rb_irq_work *work;
531        int ret = 0;
532
533        /*
534         * Depending on what the caller is waiting for, either any
535         * data in any cpu buffer, or a specific buffer, put the
536         * caller on the appropriate wait queue.
537         */
538        if (cpu == RING_BUFFER_ALL_CPUS) {
539                work = &buffer->irq_work;
540                /* Full only makes sense on per cpu reads */
541                full = false;
542        } else {
543                if (!cpumask_test_cpu(cpu, buffer->cpumask))
544                        return -ENODEV;
545                cpu_buffer = buffer->buffers[cpu];
546                work = &cpu_buffer->irq_work;
547        }
548
549
550        while (true) {
551                if (full)
552                        prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
553                else
554                        prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
555
556                /*
557                 * The events can happen in critical sections where
558                 * checking a work queue can cause deadlocks.
559                 * After adding a task to the queue, this flag is set
560                 * only to notify events to try to wake up the queue
561                 * using irq_work.
562                 *
563                 * We don't clear it even if the buffer is no longer
564                 * empty. The flag only causes the next event to run
565                 * irq_work to do the work queue wake up. The worse
566                 * that can happen if we race with !trace_empty() is that
567                 * an event will cause an irq_work to try to wake up
568                 * an empty queue.
569                 *
570                 * There's no reason to protect this flag either, as
571                 * the work queue and irq_work logic will do the necessary
572                 * synchronization for the wake ups. The only thing
573                 * that is necessary is that the wake up happens after
574                 * a task has been queued. It's OK for spurious wake ups.
575                 */
576                if (full)
577                        work->full_waiters_pending = true;
578                else
579                        work->waiters_pending = true;
580
581                if (signal_pending(current)) {
582                        ret = -EINTR;
583                        break;
584                }
585
586                if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
587                        break;
588
589                if (cpu != RING_BUFFER_ALL_CPUS &&
590                    !ring_buffer_empty_cpu(buffer, cpu)) {
591                        unsigned long flags;
592                        bool pagebusy;
593
594                        if (!full)
595                                break;
596
597                        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
598                        pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
599                        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
600
601                        if (!pagebusy)
602                                break;
603                }
604
605                schedule();
606        }
607
608        if (full)
609                finish_wait(&work->full_waiters, &wait);
610        else
611                finish_wait(&work->waiters, &wait);
612
613        return ret;
614}
615
616/**
617 * ring_buffer_poll_wait - poll on buffer input
618 * @buffer: buffer to wait on
619 * @cpu: the cpu buffer to wait on
620 * @filp: the file descriptor
621 * @poll_table: The poll descriptor
622 *
623 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
624 * as data is added to any of the @buffer's cpu buffers. Otherwise
625 * it will wait for data to be added to a specific cpu buffer.
626 *
627 * Returns POLLIN | POLLRDNORM if data exists in the buffers,
628 * zero otherwise.
629 */
630int ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
631                          struct file *filp, poll_table *poll_table)
632{
633        struct ring_buffer_per_cpu *cpu_buffer;
634        struct rb_irq_work *work;
635
636        if (cpu == RING_BUFFER_ALL_CPUS)
637                work = &buffer->irq_work;
638        else {
639                if (!cpumask_test_cpu(cpu, buffer->cpumask))
640                        return -EINVAL;
641
642                cpu_buffer = buffer->buffers[cpu];
643                work = &cpu_buffer->irq_work;
644        }
645
646        poll_wait(filp, &work->waiters, poll_table);
647        work->waiters_pending = true;
648        /*
649         * There's a tight race between setting the waiters_pending and
650         * checking if the ring buffer is empty.  Once the waiters_pending bit
651         * is set, the next event will wake the task up, but we can get stuck
652         * if there's only a single event in.
653         *
654         * FIXME: Ideally, we need a memory barrier on the writer side as well,
655         * but adding a memory barrier to all events will cause too much of a
656         * performance hit in the fast path.  We only need a memory barrier when
657         * the buffer goes from empty to having content.  But as this race is
658         * extremely small, and it's not a problem if another event comes in, we
659         * will fix it later.
660         */
661        smp_mb();
662
663        if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
664            (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
665                return POLLIN | POLLRDNORM;
666        return 0;
667}
668
669/* buffer may be either ring_buffer or ring_buffer_per_cpu */
670#define RB_WARN_ON(b, cond)                                             \
671        ({                                                              \
672                int _____ret = unlikely(cond);                          \
673                if (_____ret) {                                         \
674                        if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
675                                struct ring_buffer_per_cpu *__b =       \
676                                        (void *)b;                      \
677                                atomic_inc(&__b->buffer->record_disabled); \
678                        } else                                          \
679                                atomic_inc(&b->record_disabled);        \
680                        WARN_ON(1);                                     \
681                }                                                       \
682                _____ret;                                               \
683        })
684
685/* Up this if you want to test the TIME_EXTENTS and normalization */
686#define DEBUG_SHIFT 0
687
688static inline u64 rb_time_stamp(struct ring_buffer *buffer)
689{
690        /* shift to debug/test normalization and TIME_EXTENTS */
691        return buffer->clock() << DEBUG_SHIFT;
692}
693
694u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
695{
696        u64 time;
697
698        preempt_disable_notrace();
699        time = rb_time_stamp(buffer);
700        preempt_enable_no_resched_notrace();
701
702        return time;
703}
704EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
705
706void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
707                                      int cpu, u64 *ts)
708{
709        /* Just stupid testing the normalize function and deltas */
710        *ts >>= DEBUG_SHIFT;
711}
712EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
713
714/*
715 * Making the ring buffer lockless makes things tricky.
716 * Although writes only happen on the CPU that they are on,
717 * and they only need to worry about interrupts. Reads can
718 * happen on any CPU.
719 *
720 * The reader page is always off the ring buffer, but when the
721 * reader finishes with a page, it needs to swap its page with
722 * a new one from the buffer. The reader needs to take from
723 * the head (writes go to the tail). But if a writer is in overwrite
724 * mode and wraps, it must push the head page forward.
725 *
726 * Here lies the problem.
727 *
728 * The reader must be careful to replace only the head page, and
729 * not another one. As described at the top of the file in the
730 * ASCII art, the reader sets its old page to point to the next
731 * page after head. It then sets the page after head to point to
732 * the old reader page. But if the writer moves the head page
733 * during this operation, the reader could end up with the tail.
734 *
735 * We use cmpxchg to help prevent this race. We also do something
736 * special with the page before head. We set the LSB to 1.
737 *
738 * When the writer must push the page forward, it will clear the
739 * bit that points to the head page, move the head, and then set
740 * the bit that points to the new head page.
741 *
742 * We also don't want an interrupt coming in and moving the head
743 * page on another writer. Thus we use the second LSB to catch
744 * that too. Thus:
745 *
746 * head->list->prev->next        bit 1          bit 0
747 *                              -------        -------
748 * Normal page                     0              0
749 * Points to head page             0              1
750 * New head page                   1              0
751 *
752 * Note we can not trust the prev pointer of the head page, because:
753 *
754 * +----+       +-----+        +-----+
755 * |    |------>|  T  |---X--->|  N  |
756 * |    |<------|     |        |     |
757 * +----+       +-----+        +-----+
758 *   ^                           ^ |
759 *   |          +-----+          | |
760 *   +----------|  R  |----------+ |
761 *              |     |<-----------+
762 *              +-----+
763 *
764 * Key:  ---X-->  HEAD flag set in pointer
765 *         T      Tail page
766 *         R      Reader page
767 *         N      Next page
768 *
769 * (see __rb_reserve_next() to see where this happens)
770 *
771 *  What the above shows is that the reader just swapped out
772 *  the reader page with a page in the buffer, but before it
773 *  could make the new header point back to the new page added
774 *  it was preempted by a writer. The writer moved forward onto
775 *  the new page added by the reader and is about to move forward
776 *  again.
777 *
778 *  You can see, it is legitimate for the previous pointer of
779 *  the head (or any page) not to point back to itself. But only
780 *  temporarially.
781 */
782
783#define RB_PAGE_NORMAL          0UL
784#define RB_PAGE_HEAD            1UL
785#define RB_PAGE_UPDATE          2UL
786
787
788#define RB_FLAG_MASK            3UL
789
790/* PAGE_MOVED is not part of the mask */
791#define RB_PAGE_MOVED           4UL
792
793/*
794 * rb_list_head - remove any bit
795 */
796static struct list_head *rb_list_head(struct list_head *list)
797{
798        unsigned long val = (unsigned long)list;
799
800        return (struct list_head *)(val & ~RB_FLAG_MASK);
801}
802
803/*
804 * rb_is_head_page - test if the given page is the head page
805 *
806 * Because the reader may move the head_page pointer, we can
807 * not trust what the head page is (it may be pointing to
808 * the reader page). But if the next page is a header page,
809 * its flags will be non zero.
810 */
811static inline int
812rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
813                struct buffer_page *page, struct list_head *list)
814{
815        unsigned long val;
816
817        val = (unsigned long)list->next;
818
819        if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
820                return RB_PAGE_MOVED;
821
822        return val & RB_FLAG_MASK;
823}
824
825/*
826 * rb_is_reader_page
827 *
828 * The unique thing about the reader page, is that, if the
829 * writer is ever on it, the previous pointer never points
830 * back to the reader page.
831 */
832static bool rb_is_reader_page(struct buffer_page *page)
833{
834        struct list_head *list = page->list.prev;
835
836        return rb_list_head(list->next) != &page->list;
837}
838
839/*
840 * rb_set_list_to_head - set a list_head to be pointing to head.
841 */
842static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
843                                struct list_head *list)
844{
845        unsigned long *ptr;
846
847        ptr = (unsigned long *)&list->next;
848        *ptr |= RB_PAGE_HEAD;
849        *ptr &= ~RB_PAGE_UPDATE;
850}
851
852/*
853 * rb_head_page_activate - sets up head page
854 */
855static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
856{
857        struct buffer_page *head;
858
859        head = cpu_buffer->head_page;
860        if (!head)
861                return;
862
863        /*
864         * Set the previous list pointer to have the HEAD flag.
865         */
866        rb_set_list_to_head(cpu_buffer, head->list.prev);
867}
868
869static void rb_list_head_clear(struct list_head *list)
870{
871        unsigned long *ptr = (unsigned long *)&list->next;
872
873        *ptr &= ~RB_FLAG_MASK;
874}
875
876/*
877 * rb_head_page_dactivate - clears head page ptr (for free list)
878 */
879static void
880rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
881{
882        struct list_head *hd;
883
884        /* Go through the whole list and clear any pointers found. */
885        rb_list_head_clear(cpu_buffer->pages);
886
887        list_for_each(hd, cpu_buffer->pages)
888                rb_list_head_clear(hd);
889}
890
891static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
892                            struct buffer_page *head,
893                            struct buffer_page *prev,
894                            int old_flag, int new_flag)
895{
896        struct list_head *list;
897        unsigned long val = (unsigned long)&head->list;
898        unsigned long ret;
899
900        list = &prev->list;
901
902        val &= ~RB_FLAG_MASK;
903
904        ret = cmpxchg((unsigned long *)&list->next,
905                      val | old_flag, val | new_flag);
906
907        /* check if the reader took the page */
908        if ((ret & ~RB_FLAG_MASK) != val)
909                return RB_PAGE_MOVED;
910
911        return ret & RB_FLAG_MASK;
912}
913
914static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
915                                   struct buffer_page *head,
916                                   struct buffer_page *prev,
917                                   int old_flag)
918{
919        return rb_head_page_set(cpu_buffer, head, prev,
920                                old_flag, RB_PAGE_UPDATE);
921}
922
923static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
924                                 struct buffer_page *head,
925                                 struct buffer_page *prev,
926                                 int old_flag)
927{
928        return rb_head_page_set(cpu_buffer, head, prev,
929                                old_flag, RB_PAGE_HEAD);
930}
931
932static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
933                                   struct buffer_page *head,
934                                   struct buffer_page *prev,
935                                   int old_flag)
936{
937        return rb_head_page_set(cpu_buffer, head, prev,
938                                old_flag, RB_PAGE_NORMAL);
939}
940
941static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
942                               struct buffer_page **bpage)
943{
944        struct list_head *p = rb_list_head((*bpage)->list.next);
945
946        *bpage = list_entry(p, struct buffer_page, list);
947}
948
949static struct buffer_page *
950rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
951{
952        struct buffer_page *head;
953        struct buffer_page *page;
954        struct list_head *list;
955        int i;
956
957        if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
958                return NULL;
959
960        /* sanity check */
961        list = cpu_buffer->pages;
962        if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
963                return NULL;
964
965        page = head = cpu_buffer->head_page;
966        /*
967         * It is possible that the writer moves the header behind
968         * where we started, and we miss in one loop.
969         * A second loop should grab the header, but we'll do
970         * three loops just because I'm paranoid.
971         */
972        for (i = 0; i < 3; i++) {
973                do {
974                        if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
975                                cpu_buffer->head_page = page;
976                                return page;
977                        }
978                        rb_inc_page(cpu_buffer, &page);
979                } while (page != head);
980        }
981
982        RB_WARN_ON(cpu_buffer, 1);
983
984        return NULL;
985}
986
987static int rb_head_page_replace(struct buffer_page *old,
988                                struct buffer_page *new)
989{
990        unsigned long *ptr = (unsigned long *)&old->list.prev->next;
991        unsigned long val;
992        unsigned long ret;
993
994        val = *ptr & ~RB_FLAG_MASK;
995        val |= RB_PAGE_HEAD;
996
997        ret = cmpxchg(ptr, val, (unsigned long)&new->list);
998
999        return ret == val;
1000}
1001
1002/*
1003 * rb_tail_page_update - move the tail page forward
1004 *
1005 * Returns 1 if moved tail page, 0 if someone else did.
1006 */
1007static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
1008                               struct buffer_page *tail_page,
1009                               struct buffer_page *next_page)
1010{
1011        struct buffer_page *old_tail;
1012        unsigned long old_entries;
1013        unsigned long old_write;
1014        int ret = 0;
1015
1016        /*
1017         * The tail page now needs to be moved forward.
1018         *
1019         * We need to reset the tail page, but without messing
1020         * with possible erasing of data brought in by interrupts
1021         * that have moved the tail page and are currently on it.
1022         *
1023         * We add a counter to the write field to denote this.
1024         */
1025        old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1026        old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1027
1028        /*
1029         * Just make sure we have seen our old_write and synchronize
1030         * with any interrupts that come in.
1031         */
1032        barrier();
1033
1034        /*
1035         * If the tail page is still the same as what we think
1036         * it is, then it is up to us to update the tail
1037         * pointer.
1038         */
1039        if (tail_page == cpu_buffer->tail_page) {
1040                /* Zero the write counter */
1041                unsigned long val = old_write & ~RB_WRITE_MASK;
1042                unsigned long eval = old_entries & ~RB_WRITE_MASK;
1043
1044                /*
1045                 * This will only succeed if an interrupt did
1046                 * not come in and change it. In which case, we
1047                 * do not want to modify it.
1048                 *
1049                 * We add (void) to let the compiler know that we do not care
1050                 * about the return value of these functions. We use the
1051                 * cmpxchg to only update if an interrupt did not already
1052                 * do it for us. If the cmpxchg fails, we don't care.
1053                 */
1054                (void)local_cmpxchg(&next_page->write, old_write, val);
1055                (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1056
1057                /*
1058                 * No need to worry about races with clearing out the commit.
1059                 * it only can increment when a commit takes place. But that
1060                 * only happens in the outer most nested commit.
1061                 */
1062                local_set(&next_page->page->commit, 0);
1063
1064                old_tail = cmpxchg(&cpu_buffer->tail_page,
1065                                   tail_page, next_page);
1066
1067                if (old_tail == tail_page)
1068                        ret = 1;
1069        }
1070
1071        return ret;
1072}
1073
1074static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1075                          struct buffer_page *bpage)
1076{
1077        unsigned long val = (unsigned long)bpage;
1078
1079        if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1080                return 1;
1081
1082        return 0;
1083}
1084
1085/**
1086 * rb_check_list - make sure a pointer to a list has the last bits zero
1087 */
1088static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1089                         struct list_head *list)
1090{
1091        if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1092                return 1;
1093        if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1094                return 1;
1095        return 0;
1096}
1097
1098/**
1099 * rb_check_pages - integrity check of buffer pages
1100 * @cpu_buffer: CPU buffer with pages to test
1101 *
1102 * As a safety measure we check to make sure the data pages have not
1103 * been corrupted.
1104 */
1105static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1106{
1107        struct list_head *head = cpu_buffer->pages;
1108        struct buffer_page *bpage, *tmp;
1109
1110        /* Reset the head page if it exists */
1111        if (cpu_buffer->head_page)
1112                rb_set_head_page(cpu_buffer);
1113
1114        rb_head_page_deactivate(cpu_buffer);
1115
1116        if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1117                return -1;
1118        if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1119                return -1;
1120
1121        if (rb_check_list(cpu_buffer, head))
1122                return -1;
1123
1124        list_for_each_entry_safe(bpage, tmp, head, list) {
1125                if (RB_WARN_ON(cpu_buffer,
1126                               bpage->list.next->prev != &bpage->list))
1127                        return -1;
1128                if (RB_WARN_ON(cpu_buffer,
1129                               bpage->list.prev->next != &bpage->list))
1130                        return -1;
1131                if (rb_check_list(cpu_buffer, &bpage->list))
1132                        return -1;
1133        }
1134
1135        rb_head_page_activate(cpu_buffer);
1136
1137        return 0;
1138}
1139
1140static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
1141{
1142        struct buffer_page *bpage, *tmp;
1143        long i;
1144
1145        for (i = 0; i < nr_pages; i++) {
1146                struct page *page;
1147                /*
1148                 * __GFP_NORETRY flag makes sure that the allocation fails
1149                 * gracefully without invoking oom-killer and the system is
1150                 * not destabilized.
1151                 */
1152                bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1153                                    GFP_KERNEL | __GFP_NORETRY,
1154                                    cpu_to_node(cpu));
1155                if (!bpage)
1156                        goto free_pages;
1157
1158                list_add(&bpage->list, pages);
1159
1160                page = alloc_pages_node(cpu_to_node(cpu),
1161                                        GFP_KERNEL | __GFP_NORETRY, 0);
1162                if (!page)
1163                        goto free_pages;
1164                bpage->page = page_address(page);
1165                rb_init_page(bpage->page);
1166        }
1167
1168        return 0;
1169
1170free_pages:
1171        list_for_each_entry_safe(bpage, tmp, pages, list) {
1172                list_del_init(&bpage->list);
1173                free_buffer_page(bpage);
1174        }
1175
1176        return -ENOMEM;
1177}
1178
1179static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1180                             unsigned long nr_pages)
1181{
1182        LIST_HEAD(pages);
1183
1184        WARN_ON(!nr_pages);
1185
1186        if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1187                return -ENOMEM;
1188
1189        /*
1190         * The ring buffer page list is a circular list that does not
1191         * start and end with a list head. All page list items point to
1192         * other pages.
1193         */
1194        cpu_buffer->pages = pages.next;
1195        list_del(&pages);
1196
1197        cpu_buffer->nr_pages = nr_pages;
1198
1199        rb_check_pages(cpu_buffer);
1200
1201        return 0;
1202}
1203
1204static struct ring_buffer_per_cpu *
1205rb_allocate_cpu_buffer(struct ring_buffer *buffer, long nr_pages, int cpu)
1206{
1207        struct ring_buffer_per_cpu *cpu_buffer;
1208        struct buffer_page *bpage;
1209        struct page *page;
1210        int ret;
1211
1212        cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1213                                  GFP_KERNEL, cpu_to_node(cpu));
1214        if (!cpu_buffer)
1215                return NULL;
1216
1217        cpu_buffer->cpu = cpu;
1218        cpu_buffer->buffer = buffer;
1219        raw_spin_lock_init(&cpu_buffer->reader_lock);
1220        lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1221        cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1222        INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1223        init_completion(&cpu_buffer->update_done);
1224        init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1225        init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1226        init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1227
1228        bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1229                            GFP_KERNEL, cpu_to_node(cpu));
1230        if (!bpage)
1231                goto fail_free_buffer;
1232
1233        rb_check_bpage(cpu_buffer, bpage);
1234
1235        cpu_buffer->reader_page = bpage;
1236        page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1237        if (!page)
1238                goto fail_free_reader;
1239        bpage->page = page_address(page);
1240        rb_init_page(bpage->page);
1241
1242        INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1243        INIT_LIST_HEAD(&cpu_buffer->new_pages);
1244
1245        ret = rb_allocate_pages(cpu_buffer, nr_pages);
1246        if (ret < 0)
1247                goto fail_free_reader;
1248
1249        cpu_buffer->head_page
1250                = list_entry(cpu_buffer->pages, struct buffer_page, list);
1251        cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1252
1253        rb_head_page_activate(cpu_buffer);
1254
1255        return cpu_buffer;
1256
1257 fail_free_reader:
1258        free_buffer_page(cpu_buffer->reader_page);
1259
1260 fail_free_buffer:
1261        kfree(cpu_buffer);
1262        return NULL;
1263}
1264
1265static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1266{
1267        struct list_head *head = cpu_buffer->pages;
1268        struct buffer_page *bpage, *tmp;
1269
1270        free_buffer_page(cpu_buffer->reader_page);
1271
1272        rb_head_page_deactivate(cpu_buffer);
1273
1274        if (head) {
1275                list_for_each_entry_safe(bpage, tmp, head, list) {
1276                        list_del_init(&bpage->list);
1277                        free_buffer_page(bpage);
1278                }
1279                bpage = list_entry(head, struct buffer_page, list);
1280                free_buffer_page(bpage);
1281        }
1282
1283        kfree(cpu_buffer);
1284}
1285
1286#ifdef CONFIG_HOTPLUG_CPU
1287static int rb_cpu_notify(struct notifier_block *self,
1288                         unsigned long action, void *hcpu);
1289#endif
1290
1291/**
1292 * __ring_buffer_alloc - allocate a new ring_buffer
1293 * @size: the size in bytes per cpu that is needed.
1294 * @flags: attributes to set for the ring buffer.
1295 *
1296 * Currently the only flag that is available is the RB_FL_OVERWRITE
1297 * flag. This flag means that the buffer will overwrite old data
1298 * when the buffer wraps. If this flag is not set, the buffer will
1299 * drop data when the tail hits the head.
1300 */
1301struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1302                                        struct lock_class_key *key)
1303{
1304        struct ring_buffer *buffer;
1305        long nr_pages;
1306        int bsize;
1307        int cpu;
1308
1309        /* keep it in its own cache line */
1310        buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1311                         GFP_KERNEL);
1312        if (!buffer)
1313                return NULL;
1314
1315        if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1316                goto fail_free_buffer;
1317
1318        nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1319        buffer->flags = flags;
1320        buffer->clock = trace_clock_local;
1321        buffer->reader_lock_key = key;
1322
1323        init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1324        init_waitqueue_head(&buffer->irq_work.waiters);
1325
1326        /* need at least two pages */
1327        if (nr_pages < 2)
1328                nr_pages = 2;
1329
1330        /*
1331         * In case of non-hotplug cpu, if the ring-buffer is allocated
1332         * in early initcall, it will not be notified of secondary cpus.
1333         * In that off case, we need to allocate for all possible cpus.
1334         */
1335#ifdef CONFIG_HOTPLUG_CPU
1336        cpu_notifier_register_begin();
1337        cpumask_copy(buffer->cpumask, cpu_online_mask);
1338#else
1339        cpumask_copy(buffer->cpumask, cpu_possible_mask);
1340#endif
1341        buffer->cpus = nr_cpu_ids;
1342
1343        bsize = sizeof(void *) * nr_cpu_ids;
1344        buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1345                                  GFP_KERNEL);
1346        if (!buffer->buffers)
1347                goto fail_free_cpumask;
1348
1349        for_each_buffer_cpu(buffer, cpu) {
1350                buffer->buffers[cpu] =
1351                        rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1352                if (!buffer->buffers[cpu])
1353                        goto fail_free_buffers;
1354        }
1355
1356#ifdef CONFIG_HOTPLUG_CPU
1357        buffer->cpu_notify.notifier_call = rb_cpu_notify;
1358        buffer->cpu_notify.priority = 0;
1359        __register_cpu_notifier(&buffer->cpu_notify);
1360        cpu_notifier_register_done();
1361#endif
1362
1363        mutex_init(&buffer->mutex);
1364
1365        return buffer;
1366
1367 fail_free_buffers:
1368        for_each_buffer_cpu(buffer, cpu) {
1369                if (buffer->buffers[cpu])
1370                        rb_free_cpu_buffer(buffer->buffers[cpu]);
1371        }
1372        kfree(buffer->buffers);
1373
1374 fail_free_cpumask:
1375        free_cpumask_var(buffer->cpumask);
1376#ifdef CONFIG_HOTPLUG_CPU
1377        cpu_notifier_register_done();
1378#endif
1379
1380 fail_free_buffer:
1381        kfree(buffer);
1382        return NULL;
1383}
1384EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1385
1386/**
1387 * ring_buffer_free - free a ring buffer.
1388 * @buffer: the buffer to free.
1389 */
1390void
1391ring_buffer_free(struct ring_buffer *buffer)
1392{
1393        int cpu;
1394
1395#ifdef CONFIG_HOTPLUG_CPU
1396        cpu_notifier_register_begin();
1397        __unregister_cpu_notifier(&buffer->cpu_notify);
1398#endif
1399
1400        for_each_buffer_cpu(buffer, cpu)
1401                rb_free_cpu_buffer(buffer->buffers[cpu]);
1402
1403#ifdef CONFIG_HOTPLUG_CPU
1404        cpu_notifier_register_done();
1405#endif
1406
1407        kfree(buffer->buffers);
1408        free_cpumask_var(buffer->cpumask);
1409
1410        kfree(buffer);
1411}
1412EXPORT_SYMBOL_GPL(ring_buffer_free);
1413
1414void ring_buffer_set_clock(struct ring_buffer *buffer,
1415                           u64 (*clock)(void))
1416{
1417        buffer->clock = clock;
1418}
1419
1420static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1421
1422static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1423{
1424        return local_read(&bpage->entries) & RB_WRITE_MASK;
1425}
1426
1427static inline unsigned long rb_page_write(struct buffer_page *bpage)
1428{
1429        return local_read(&bpage->write) & RB_WRITE_MASK;
1430}
1431
1432static int
1433rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
1434{
1435        struct list_head *tail_page, *to_remove, *next_page;
1436        struct buffer_page *to_remove_page, *tmp_iter_page;
1437        struct buffer_page *last_page, *first_page;
1438        unsigned long nr_removed;
1439        unsigned long head_bit;
1440        int page_entries;
1441
1442        head_bit = 0;
1443
1444        raw_spin_lock_irq(&cpu_buffer->reader_lock);
1445        atomic_inc(&cpu_buffer->record_disabled);
1446        /*
1447         * We don't race with the readers since we have acquired the reader
1448         * lock. We also don't race with writers after disabling recording.
1449         * This makes it easy to figure out the first and the last page to be
1450         * removed from the list. We unlink all the pages in between including
1451         * the first and last pages. This is done in a busy loop so that we
1452         * lose the least number of traces.
1453         * The pages are freed after we restart recording and unlock readers.
1454         */
1455        tail_page = &cpu_buffer->tail_page->list;
1456
1457        /*
1458         * tail page might be on reader page, we remove the next page
1459         * from the ring buffer
1460         */
1461        if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1462                tail_page = rb_list_head(tail_page->next);
1463        to_remove = tail_page;
1464
1465        /* start of pages to remove */
1466        first_page = list_entry(rb_list_head(to_remove->next),
1467                                struct buffer_page, list);
1468
1469        for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1470                to_remove = rb_list_head(to_remove)->next;
1471                head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1472        }
1473
1474        next_page = rb_list_head(to_remove)->next;
1475
1476        /*
1477         * Now we remove all pages between tail_page and next_page.
1478         * Make sure that we have head_bit value preserved for the
1479         * next page
1480         */
1481        tail_page->next = (struct list_head *)((unsigned long)next_page |
1482                                                head_bit);
1483        next_page = rb_list_head(next_page);
1484        next_page->prev = tail_page;
1485
1486        /* make sure pages points to a valid page in the ring buffer */
1487        cpu_buffer->pages = next_page;
1488
1489        /* update head page */
1490        if (head_bit)
1491                cpu_buffer->head_page = list_entry(next_page,
1492                                                struct buffer_page, list);
1493
1494        /*
1495         * change read pointer to make sure any read iterators reset
1496         * themselves
1497         */
1498        cpu_buffer->read = 0;
1499
1500        /* pages are removed, resume tracing and then free the pages */
1501        atomic_dec(&cpu_buffer->record_disabled);
1502        raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1503
1504        RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1505
1506        /* last buffer page to remove */
1507        last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1508                                list);
1509        tmp_iter_page = first_page;
1510
1511        do {
1512                to_remove_page = tmp_iter_page;
1513                rb_inc_page(cpu_buffer, &tmp_iter_page);
1514
1515                /* update the counters */
1516                page_entries = rb_page_entries(to_remove_page);
1517                if (page_entries) {
1518                        /*
1519                         * If something was added to this page, it was full
1520                         * since it is not the tail page. So we deduct the
1521                         * bytes consumed in ring buffer from here.
1522                         * Increment overrun to account for the lost events.
1523                         */
1524                        local_add(page_entries, &cpu_buffer->overrun);
1525                        local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1526                }
1527
1528                /*
1529                 * We have already removed references to this list item, just
1530                 * free up the buffer_page and its page
1531                 */
1532                free_buffer_page(to_remove_page);
1533                nr_removed--;
1534
1535        } while (to_remove_page != last_page);
1536
1537        RB_WARN_ON(cpu_buffer, nr_removed);
1538
1539        return nr_removed == 0;
1540}
1541
1542static int
1543rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1544{
1545        struct list_head *pages = &cpu_buffer->new_pages;
1546        int retries, success;
1547
1548        raw_spin_lock_irq(&cpu_buffer->reader_lock);
1549        /*
1550         * We are holding the reader lock, so the reader page won't be swapped
1551         * in the ring buffer. Now we are racing with the writer trying to
1552         * move head page and the tail page.
1553         * We are going to adapt the reader page update process where:
1554         * 1. We first splice the start and end of list of new pages between
1555         *    the head page and its previous page.
1556         * 2. We cmpxchg the prev_page->next to point from head page to the
1557         *    start of new pages list.
1558         * 3. Finally, we update the head->prev to the end of new list.
1559         *
1560         * We will try this process 10 times, to make sure that we don't keep
1561         * spinning.
1562         */
1563        retries = 10;
1564        success = 0;
1565        while (retries--) {
1566                struct list_head *head_page, *prev_page, *r;
1567                struct list_head *last_page, *first_page;
1568                struct list_head *head_page_with_bit;
1569
1570                head_page = &rb_set_head_page(cpu_buffer)->list;
1571                if (!head_page)
1572                        break;
1573                prev_page = head_page->prev;
1574
1575                first_page = pages->next;
1576                last_page  = pages->prev;
1577
1578                head_page_with_bit = (struct list_head *)
1579                                     ((unsigned long)head_page | RB_PAGE_HEAD);
1580
1581                last_page->next = head_page_with_bit;
1582                first_page->prev = prev_page;
1583
1584                r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1585
1586                if (r == head_page_with_bit) {
1587                        /*
1588                         * yay, we replaced the page pointer to our new list,
1589                         * now, we just have to update to head page's prev
1590                         * pointer to point to end of list
1591                         */
1592                        head_page->prev = last_page;
1593                        success = 1;
1594                        break;
1595                }
1596        }
1597
1598        if (success)
1599                INIT_LIST_HEAD(pages);
1600        /*
1601         * If we weren't successful in adding in new pages, warn and stop
1602         * tracing
1603         */
1604        RB_WARN_ON(cpu_buffer, !success);
1605        raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1606
1607        /* free pages if they weren't inserted */
1608        if (!success) {
1609                struct buffer_page *bpage, *tmp;
1610                list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1611                                         list) {
1612                        list_del_init(&bpage->list);
1613                        free_buffer_page(bpage);
1614                }
1615        }
1616        return success;
1617}
1618
1619static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1620{
1621        int success;
1622
1623        if (cpu_buffer->nr_pages_to_update > 0)
1624                success = rb_insert_pages(cpu_buffer);
1625        else
1626                success = rb_remove_pages(cpu_buffer,
1627                                        -cpu_buffer->nr_pages_to_update);
1628
1629        if (success)
1630                cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1631}
1632
1633static void update_pages_handler(struct work_struct *work)
1634{
1635        struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1636                        struct ring_buffer_per_cpu, update_pages_work);
1637        rb_update_pages(cpu_buffer);
1638        complete(&cpu_buffer->update_done);
1639}
1640
1641/**
1642 * ring_buffer_resize - resize the ring buffer
1643 * @buffer: the buffer to resize.
1644 * @size: the new size.
1645 * @cpu_id: the cpu buffer to resize
1646 *
1647 * Minimum size is 2 * BUF_PAGE_SIZE.
1648 *
1649 * Returns 0 on success and < 0 on failure.
1650 */
1651int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1652                        int cpu_id)
1653{
1654        struct ring_buffer_per_cpu *cpu_buffer;
1655        unsigned long nr_pages;
1656        int cpu, err = 0;
1657
1658        /*
1659         * Always succeed at resizing a non-existent buffer:
1660         */
1661        if (!buffer)
1662                return size;
1663
1664        /* Make sure the requested buffer exists */
1665        if (cpu_id != RING_BUFFER_ALL_CPUS &&
1666            !cpumask_test_cpu(cpu_id, buffer->cpumask))
1667                return size;
1668
1669        nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1670
1671        /* we need a minimum of two pages */
1672        if (nr_pages < 2)
1673                nr_pages = 2;
1674
1675        size = nr_pages * BUF_PAGE_SIZE;
1676
1677        /*
1678         * Don't succeed if resizing is disabled, as a reader might be
1679         * manipulating the ring buffer and is expecting a sane state while
1680         * this is true.
1681         */
1682        if (atomic_read(&buffer->resize_disabled))
1683                return -EBUSY;
1684
1685        /* prevent another thread from changing buffer sizes */
1686        mutex_lock(&buffer->mutex);
1687
1688        if (cpu_id == RING_BUFFER_ALL_CPUS) {
1689                /* calculate the pages to update */
1690                for_each_buffer_cpu(buffer, cpu) {
1691                        cpu_buffer = buffer->buffers[cpu];
1692
1693                        cpu_buffer->nr_pages_to_update = nr_pages -
1694                                                        cpu_buffer->nr_pages;
1695                        /*
1696                         * nothing more to do for removing pages or no update
1697                         */
1698                        if (cpu_buffer->nr_pages_to_update <= 0)
1699                                continue;
1700                        /*
1701                         * to add pages, make sure all new pages can be
1702                         * allocated without receiving ENOMEM
1703                         */
1704                        INIT_LIST_HEAD(&cpu_buffer->new_pages);
1705                        if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1706                                                &cpu_buffer->new_pages, cpu)) {
1707                                /* not enough memory for new pages */
1708                                err = -ENOMEM;
1709                                goto out_err;
1710                        }
1711                }
1712
1713                get_online_cpus();
1714                /*
1715                 * Fire off all the required work handlers
1716                 * We can't schedule on offline CPUs, but it's not necessary
1717                 * since we can change their buffer sizes without any race.
1718                 */
1719                for_each_buffer_cpu(buffer, cpu) {
1720                        cpu_buffer = buffer->buffers[cpu];
1721                        if (!cpu_buffer->nr_pages_to_update)
1722                                continue;
1723
1724                        /* Can't run something on an offline CPU. */
1725                        if (!cpu_online(cpu)) {
1726                                rb_update_pages(cpu_buffer);
1727                                cpu_buffer->nr_pages_to_update = 0;
1728                        } else {
1729                                schedule_work_on(cpu,
1730                                                &cpu_buffer->update_pages_work);
1731                        }
1732                }
1733
1734                /* wait for all the updates to complete */
1735                for_each_buffer_cpu(buffer, cpu) {
1736                        cpu_buffer = buffer->buffers[cpu];
1737                        if (!cpu_buffer->nr_pages_to_update)
1738                                continue;
1739
1740                        if (cpu_online(cpu))
1741                                wait_for_completion(&cpu_buffer->update_done);
1742                        cpu_buffer->nr_pages_to_update = 0;
1743                }
1744
1745                put_online_cpus();
1746        } else {
1747                /* Make sure this CPU has been intitialized */
1748                if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
1749                        goto out;
1750
1751                cpu_buffer = buffer->buffers[cpu_id];
1752
1753                if (nr_pages == cpu_buffer->nr_pages)
1754                        goto out;
1755
1756                cpu_buffer->nr_pages_to_update = nr_pages -
1757                                                cpu_buffer->nr_pages;
1758
1759                INIT_LIST_HEAD(&cpu_buffer->new_pages);
1760                if (cpu_buffer->nr_pages_to_update > 0 &&
1761                        __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1762                                            &cpu_buffer->new_pages, cpu_id)) {
1763                        err = -ENOMEM;
1764                        goto out_err;
1765                }
1766
1767                get_online_cpus();
1768
1769                /* Can't run something on an offline CPU. */
1770                if (!cpu_online(cpu_id))
1771                        rb_update_pages(cpu_buffer);
1772                else {
1773                        schedule_work_on(cpu_id,
1774                                         &cpu_buffer->update_pages_work);
1775                        wait_for_completion(&cpu_buffer->update_done);
1776                }
1777
1778                cpu_buffer->nr_pages_to_update = 0;
1779                put_online_cpus();
1780        }
1781
1782 out:
1783        /*
1784         * The ring buffer resize can happen with the ring buffer
1785         * enabled, so that the update disturbs the tracing as little
1786         * as possible. But if the buffer is disabled, we do not need
1787         * to worry about that, and we can take the time to verify
1788         * that the buffer is not corrupt.
1789         */
1790        if (atomic_read(&buffer->record_disabled)) {
1791                atomic_inc(&buffer->record_disabled);
1792                /*
1793                 * Even though the buffer was disabled, we must make sure
1794                 * that it is truly disabled before calling rb_check_pages.
1795                 * There could have been a race between checking
1796                 * record_disable and incrementing it.
1797                 */
1798                synchronize_sched();
1799                for_each_buffer_cpu(buffer, cpu) {
1800                        cpu_buffer = buffer->buffers[cpu];
1801                        rb_check_pages(cpu_buffer);
1802                }
1803                atomic_dec(&buffer->record_disabled);
1804        }
1805
1806        mutex_unlock(&buffer->mutex);
1807        return size;
1808
1809 out_err:
1810        for_each_buffer_cpu(buffer, cpu) {
1811                struct buffer_page *bpage, *tmp;
1812
1813                cpu_buffer = buffer->buffers[cpu];
1814                cpu_buffer->nr_pages_to_update = 0;
1815
1816                if (list_empty(&cpu_buffer->new_pages))
1817                        continue;
1818
1819                list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1820                                        list) {
1821                        list_del_init(&bpage->list);
1822                        free_buffer_page(bpage);
1823                }
1824        }
1825        mutex_unlock(&buffer->mutex);
1826        return err;
1827}
1828EXPORT_SYMBOL_GPL(ring_buffer_resize);
1829
1830void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1831{
1832        mutex_lock(&buffer->mutex);
1833        if (val)
1834                buffer->flags |= RB_FL_OVERWRITE;
1835        else
1836                buffer->flags &= ~RB_FL_OVERWRITE;
1837        mutex_unlock(&buffer->mutex);
1838}
1839EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1840
1841static inline void *
1842__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
1843{
1844        return bpage->data + index;
1845}
1846
1847static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1848{
1849        return bpage->page->data + index;
1850}
1851
1852static inline struct ring_buffer_event *
1853rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1854{
1855        return __rb_page_index(cpu_buffer->reader_page,
1856                               cpu_buffer->reader_page->read);
1857}
1858
1859static inline struct ring_buffer_event *
1860rb_iter_head_event(struct ring_buffer_iter *iter)
1861{
1862        return __rb_page_index(iter->head_page, iter->head);
1863}
1864
1865static inline unsigned rb_page_commit(struct buffer_page *bpage)
1866{
1867        return local_read(&bpage->page->commit);
1868}
1869
1870/* Size is determined by what has been committed */
1871static inline unsigned rb_page_size(struct buffer_page *bpage)
1872{
1873        return rb_page_commit(bpage);
1874}
1875
1876static inline unsigned
1877rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1878{
1879        return rb_page_commit(cpu_buffer->commit_page);
1880}
1881
1882static inline unsigned
1883rb_event_index(struct ring_buffer_event *event)
1884{
1885        unsigned long addr = (unsigned long)event;
1886
1887        return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1888}
1889
1890static void rb_inc_iter(struct ring_buffer_iter *iter)
1891{
1892        struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1893
1894        /*
1895         * The iterator could be on the reader page (it starts there).
1896         * But the head could have moved, since the reader was
1897         * found. Check for this case and assign the iterator
1898         * to the head page instead of next.
1899         */
1900        if (iter->head_page == cpu_buffer->reader_page)
1901                iter->head_page = rb_set_head_page(cpu_buffer);
1902        else
1903                rb_inc_page(cpu_buffer, &iter->head_page);
1904
1905        iter->read_stamp = iter->head_page->page->time_stamp;
1906        iter->head = 0;
1907}
1908
1909/*
1910 * rb_handle_head_page - writer hit the head page
1911 *
1912 * Returns: +1 to retry page
1913 *           0 to continue
1914 *          -1 on error
1915 */
1916static int
1917rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
1918                    struct buffer_page *tail_page,
1919                    struct buffer_page *next_page)
1920{
1921        struct buffer_page *new_head;
1922        int entries;
1923        int type;
1924        int ret;
1925
1926        entries = rb_page_entries(next_page);
1927
1928        /*
1929         * The hard part is here. We need to move the head
1930         * forward, and protect against both readers on
1931         * other CPUs and writers coming in via interrupts.
1932         */
1933        type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
1934                                       RB_PAGE_HEAD);
1935
1936        /*
1937         * type can be one of four:
1938         *  NORMAL - an interrupt already moved it for us
1939         *  HEAD   - we are the first to get here.
1940         *  UPDATE - we are the interrupt interrupting
1941         *           a current move.
1942         *  MOVED  - a reader on another CPU moved the next
1943         *           pointer to its reader page. Give up
1944         *           and try again.
1945         */
1946
1947        switch (type) {
1948        case RB_PAGE_HEAD:
1949                /*
1950                 * We changed the head to UPDATE, thus
1951                 * it is our responsibility to update
1952                 * the counters.
1953                 */
1954                local_add(entries, &cpu_buffer->overrun);
1955                local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1956
1957                /*
1958                 * The entries will be zeroed out when we move the
1959                 * tail page.
1960                 */
1961
1962                /* still more to do */
1963                break;
1964
1965        case RB_PAGE_UPDATE:
1966                /*
1967                 * This is an interrupt that interrupt the
1968                 * previous update. Still more to do.
1969                 */
1970                break;
1971        case RB_PAGE_NORMAL:
1972                /*
1973                 * An interrupt came in before the update
1974                 * and processed this for us.
1975                 * Nothing left to do.
1976                 */
1977                return 1;
1978        case RB_PAGE_MOVED:
1979                /*
1980                 * The reader is on another CPU and just did
1981                 * a swap with our next_page.
1982                 * Try again.
1983                 */
1984                return 1;
1985        default:
1986                RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
1987                return -1;
1988        }
1989
1990        /*
1991         * Now that we are here, the old head pointer is
1992         * set to UPDATE. This will keep the reader from
1993         * swapping the head page with the reader page.
1994         * The reader (on another CPU) will spin till
1995         * we are finished.
1996         *
1997         * We just need to protect against interrupts
1998         * doing the job. We will set the next pointer
1999         * to HEAD. After that, we set the old pointer
2000         * to NORMAL, but only if it was HEAD before.
2001         * otherwise we are an interrupt, and only
2002         * want the outer most commit to reset it.
2003         */
2004        new_head = next_page;
2005        rb_inc_page(cpu_buffer, &new_head);
2006
2007        ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2008                                    RB_PAGE_NORMAL);
2009
2010        /*
2011         * Valid returns are:
2012         *  HEAD   - an interrupt came in and already set it.
2013         *  NORMAL - One of two things:
2014         *            1) We really set it.
2015         *            2) A bunch of interrupts came in and moved
2016         *               the page forward again.
2017         */
2018        switch (ret) {
2019        case RB_PAGE_HEAD:
2020        case RB_PAGE_NORMAL:
2021                /* OK */
2022                break;
2023        default:
2024                RB_WARN_ON(cpu_buffer, 1);
2025                return -1;
2026        }
2027
2028        /*
2029         * It is possible that an interrupt came in,
2030         * set the head up, then more interrupts came in
2031         * and moved it again. When we get back here,
2032         * the page would have been set to NORMAL but we
2033         * just set it back to HEAD.
2034         *
2035         * How do you detect this? Well, if that happened
2036         * the tail page would have moved.
2037         */
2038        if (ret == RB_PAGE_NORMAL) {
2039                /*
2040                 * If the tail had moved passed next, then we need
2041                 * to reset the pointer.
2042                 */
2043                if (cpu_buffer->tail_page != tail_page &&
2044                    cpu_buffer->tail_page != next_page)
2045                        rb_head_page_set_normal(cpu_buffer, new_head,
2046                                                next_page,
2047                                                RB_PAGE_HEAD);
2048        }
2049
2050        /*
2051         * If this was the outer most commit (the one that
2052         * changed the original pointer from HEAD to UPDATE),
2053         * then it is up to us to reset it to NORMAL.
2054         */
2055        if (type == RB_PAGE_HEAD) {
2056                ret = rb_head_page_set_normal(cpu_buffer, next_page,
2057                                              tail_page,
2058                                              RB_PAGE_UPDATE);
2059                if (RB_WARN_ON(cpu_buffer,
2060                               ret != RB_PAGE_UPDATE))
2061                        return -1;
2062        }
2063
2064        return 0;
2065}
2066
2067static inline void
2068rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2069              unsigned long tail, struct rb_event_info *info)
2070{
2071        struct buffer_page *tail_page = info->tail_page;
2072        struct ring_buffer_event *event;
2073        unsigned long length = info->length;
2074
2075        /*
2076         * Only the event that crossed the page boundary
2077         * must fill the old tail_page with padding.
2078         */
2079        if (tail >= BUF_PAGE_SIZE) {
2080                /*
2081                 * If the page was filled, then we still need
2082                 * to update the real_end. Reset it to zero
2083                 * and the reader will ignore it.
2084                 */
2085                if (tail == BUF_PAGE_SIZE)
2086                        tail_page->real_end = 0;
2087
2088                local_sub(length, &tail_page->write);
2089                return;
2090        }
2091
2092        event = __rb_page_index(tail_page, tail);
2093        kmemcheck_annotate_bitfield(event, bitfield);
2094
2095        /* account for padding bytes */
2096        local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2097
2098        /*
2099         * Save the original length to the meta data.
2100         * This will be used by the reader to add lost event
2101         * counter.
2102         */
2103        tail_page->real_end = tail;
2104
2105        /*
2106         * If this event is bigger than the minimum size, then
2107         * we need to be careful that we don't subtract the
2108         * write counter enough to allow another writer to slip
2109         * in on this page.
2110         * We put in a discarded commit instead, to make sure
2111         * that this space is not used again.
2112         *
2113         * If we are less than the minimum size, we don't need to
2114         * worry about it.
2115         */
2116        if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2117                /* No room for any events */
2118
2119                /* Mark the rest of the page with padding */
2120                rb_event_set_padding(event);
2121
2122                /* Set the write back to the previous setting */
2123                local_sub(length, &tail_page->write);
2124                return;
2125        }
2126
2127        /* Put in a discarded event */
2128        event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2129        event->type_len = RINGBUF_TYPE_PADDING;
2130        /* time delta must be non zero */
2131        event->time_delta = 1;
2132
2133        /* Set write to end of buffer */
2134        length = (tail + length) - BUF_PAGE_SIZE;
2135        local_sub(length, &tail_page->write);
2136}
2137
2138/*
2139 * This is the slow path, force gcc not to inline it.
2140 */
2141static noinline struct ring_buffer_event *
2142rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2143             unsigned long tail, struct rb_event_info *info)
2144{
2145        struct buffer_page *tail_page = info->tail_page;
2146        struct buffer_page *commit_page = cpu_buffer->commit_page;
2147        struct ring_buffer *buffer = cpu_buffer->buffer;
2148        struct buffer_page *next_page;
2149        int ret;
2150        u64 ts;
2151
2152        next_page = tail_page;
2153
2154        rb_inc_page(cpu_buffer, &next_page);
2155
2156        /*
2157         * If for some reason, we had an interrupt storm that made
2158         * it all the way around the buffer, bail, and warn
2159         * about it.
2160         */
2161        if (unlikely(next_page == commit_page)) {
2162                local_inc(&cpu_buffer->commit_overrun);
2163                goto out_reset;
2164        }
2165
2166        /*
2167         * This is where the fun begins!
2168         *
2169         * We are fighting against races between a reader that
2170         * could be on another CPU trying to swap its reader
2171         * page with the buffer head.
2172         *
2173         * We are also fighting against interrupts coming in and
2174         * moving the head or tail on us as well.
2175         *
2176         * If the next page is the head page then we have filled
2177         * the buffer, unless the commit page is still on the
2178         * reader page.
2179         */
2180        if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2181
2182                /*
2183                 * If the commit is not on the reader page, then
2184                 * move the header page.
2185                 */
2186                if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2187                        /*
2188                         * If we are not in overwrite mode,
2189                         * this is easy, just stop here.
2190                         */
2191                        if (!(buffer->flags & RB_FL_OVERWRITE)) {
2192                                local_inc(&cpu_buffer->dropped_events);
2193                                goto out_reset;
2194                        }
2195
2196                        ret = rb_handle_head_page(cpu_buffer,
2197                                                  tail_page,
2198                                                  next_page);
2199                        if (ret < 0)
2200                                goto out_reset;
2201                        if (ret)
2202                                goto out_again;
2203                } else {
2204                        /*
2205                         * We need to be careful here too. The
2206                         * commit page could still be on the reader
2207                         * page. We could have a small buffer, and
2208                         * have filled up the buffer with events
2209                         * from interrupts and such, and wrapped.
2210                         *
2211                         * Note, if the tail page is also the on the
2212                         * reader_page, we let it move out.
2213                         */
2214                        if (unlikely((cpu_buffer->commit_page !=
2215                                      cpu_buffer->tail_page) &&
2216                                     (cpu_buffer->commit_page ==
2217                                      cpu_buffer->reader_page))) {
2218                                local_inc(&cpu_buffer->commit_overrun);
2219                                goto out_reset;
2220                        }
2221                }
2222        }
2223
2224        ret = rb_tail_page_update(cpu_buffer, tail_page, next_page);
2225        if (ret) {
2226                /*
2227                 * Nested commits always have zero deltas, so
2228                 * just reread the time stamp
2229                 */
2230                ts = rb_time_stamp(buffer);
2231                next_page->page->time_stamp = ts;
2232        }
2233
2234 out_again:
2235
2236        rb_reset_tail(cpu_buffer, tail, info);
2237
2238        /* fail and let the caller try again */
2239        return ERR_PTR(-EAGAIN);
2240
2241 out_reset:
2242        /* reset write */
2243        rb_reset_tail(cpu_buffer, tail, info);
2244
2245        return NULL;
2246}
2247
2248/* Slow path, do not inline */
2249static noinline struct ring_buffer_event *
2250rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
2251{
2252        event->type_len = RINGBUF_TYPE_TIME_EXTEND;
2253
2254        /* Not the first event on the page? */
2255        if (rb_event_index(event)) {
2256                event->time_delta = delta & TS_MASK;
2257                event->array[0] = delta >> TS_SHIFT;
2258        } else {
2259                /* nope, just zero it */
2260                event->time_delta = 0;
2261                event->array[0] = 0;
2262        }
2263
2264        return skip_time_extend(event);
2265}
2266
2267static inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2268                                     struct ring_buffer_event *event);
2269
2270/**
2271 * rb_update_event - update event type and data
2272 * @event: the event to update
2273 * @type: the type of event
2274 * @length: the size of the event field in the ring buffer
2275 *
2276 * Update the type and data fields of the event. The length
2277 * is the actual size that is written to the ring buffer,
2278 * and with this, we can determine what to place into the
2279 * data field.
2280 */
2281static void
2282rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2283                struct ring_buffer_event *event,
2284                struct rb_event_info *info)
2285{
2286        unsigned length = info->length;
2287        u64 delta = info->delta;
2288
2289        /* Only a commit updates the timestamp */
2290        if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
2291                delta = 0;
2292
2293        /*
2294         * If we need to add a timestamp, then we
2295         * add it to the start of the resevered space.
2296         */
2297        if (unlikely(info->add_timestamp)) {
2298                event = rb_add_time_stamp(event, delta);
2299                length -= RB_LEN_TIME_EXTEND;
2300                delta = 0;
2301        }
2302
2303        event->time_delta = delta;
2304        length -= RB_EVNT_HDR_SIZE;
2305        if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2306                event->type_len = 0;
2307                event->array[0] = length;
2308        } else
2309                event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2310}
2311
2312static unsigned rb_calculate_event_length(unsigned length)
2313{
2314        struct ring_buffer_event event; /* Used only for sizeof array */
2315
2316        /* zero length can cause confusions */
2317        if (!length)
2318                length++;
2319
2320        if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2321                length += sizeof(event.array[0]);
2322
2323        length += RB_EVNT_HDR_SIZE;
2324        length = ALIGN(length, RB_ARCH_ALIGNMENT);
2325
2326        /*
2327         * In case the time delta is larger than the 27 bits for it
2328         * in the header, we need to add a timestamp. If another
2329         * event comes in when trying to discard this one to increase
2330         * the length, then the timestamp will be added in the allocated
2331         * space of this event. If length is bigger than the size needed
2332         * for the TIME_EXTEND, then padding has to be used. The events
2333         * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
2334         * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
2335         * As length is a multiple of 4, we only need to worry if it
2336         * is 12 (RB_LEN_TIME_EXTEND + 4).
2337         */
2338        if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
2339                length += RB_ALIGNMENT;
2340
2341        return length;
2342}
2343
2344#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2345static inline bool sched_clock_stable(void)
2346{
2347        return true;
2348}
2349#endif
2350
2351static inline int
2352rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2353                  struct ring_buffer_event *event)
2354{
2355        unsigned long new_index, old_index;
2356        struct buffer_page *bpage;
2357        unsigned long index;
2358        unsigned long addr;
2359
2360        new_index = rb_event_index(event);
2361        old_index = new_index + rb_event_ts_length(event);
2362        addr = (unsigned long)event;
2363        addr &= PAGE_MASK;
2364
2365        bpage = cpu_buffer->tail_page;
2366
2367        if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2368                unsigned long write_mask =
2369                        local_read(&bpage->write) & ~RB_WRITE_MASK;
2370                unsigned long event_length = rb_event_length(event);
2371                /*
2372                 * This is on the tail page. It is possible that
2373                 * a write could come in and move the tail page
2374                 * and write to the next page. That is fine
2375                 * because we just shorten what is on this page.
2376                 */
2377                old_index += write_mask;
2378                new_index += write_mask;
2379                index = local_cmpxchg(&bpage->write, old_index, new_index);
2380                if (index == old_index) {
2381                        /* update counters */
2382                        local_sub(event_length, &cpu_buffer->entries_bytes);
2383                        return 1;
2384                }
2385        }
2386
2387        /* could not discard */
2388        return 0;
2389}
2390
2391static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2392{
2393        local_inc(&cpu_buffer->committing);
2394        local_inc(&cpu_buffer->commits);
2395}
2396
2397static void
2398rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
2399{
2400        unsigned long max_count;
2401
2402        /*
2403         * We only race with interrupts and NMIs on this CPU.
2404         * If we own the commit event, then we can commit
2405         * all others that interrupted us, since the interruptions
2406         * are in stack format (they finish before they come
2407         * back to us). This allows us to do a simple loop to
2408         * assign the commit to the tail.
2409         */
2410 again:
2411        max_count = cpu_buffer->nr_pages * 100;
2412
2413        while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
2414                if (RB_WARN_ON(cpu_buffer, !(--max_count)))
2415                        return;
2416                if (RB_WARN_ON(cpu_buffer,
2417                               rb_is_reader_page(cpu_buffer->tail_page)))
2418                        return;
2419                local_set(&cpu_buffer->commit_page->page->commit,
2420                          rb_page_write(cpu_buffer->commit_page));
2421                rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
2422                cpu_buffer->write_stamp =
2423                        cpu_buffer->commit_page->page->time_stamp;
2424                /* add barrier to keep gcc from optimizing too much */
2425                barrier();
2426        }
2427        while (rb_commit_index(cpu_buffer) !=
2428               rb_page_write(cpu_buffer->commit_page)) {
2429
2430                local_set(&cpu_buffer->commit_page->page->commit,
2431                          rb_page_write(cpu_buffer->commit_page));
2432                RB_WARN_ON(cpu_buffer,
2433                           local_read(&cpu_buffer->commit_page->page->commit) &
2434                           ~RB_WRITE_MASK);
2435                barrier();
2436        }
2437
2438        /* again, keep gcc from optimizing */
2439        barrier();
2440
2441        /*
2442         * If an interrupt came in just after the first while loop
2443         * and pushed the tail page forward, we will be left with
2444         * a dangling commit that will never go forward.
2445         */
2446        if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
2447                goto again;
2448}
2449
2450static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2451{
2452        unsigned long commits;
2453
2454        if (RB_WARN_ON(cpu_buffer,
2455                       !local_read(&cpu_buffer->committing)))
2456                return;
2457
2458 again:
2459        commits = local_read(&cpu_buffer->commits);
2460        /* synchronize with interrupts */
2461        barrier();
2462        if (local_read(&cpu_buffer->committing) == 1)
2463                rb_set_commit_to_write(cpu_buffer);
2464
2465        local_dec(&cpu_buffer->committing);
2466
2467        /* synchronize with interrupts */
2468        barrier();
2469
2470        /*
2471         * Need to account for interrupts coming in between the
2472         * updating of the commit page and the clearing of the
2473         * committing counter.
2474         */
2475        if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2476            !local_read(&cpu_buffer->committing)) {
2477                local_inc(&cpu_buffer->committing);
2478                goto again;
2479        }
2480}
2481
2482static inline void rb_event_discard(struct ring_buffer_event *event)
2483{
2484        if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
2485                event = skip_time_extend(event);
2486
2487        /* array[0] holds the actual length for the discarded event */
2488        event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2489        event->type_len = RINGBUF_TYPE_PADDING;
2490        /* time delta must be non zero */
2491        if (!event->time_delta)
2492                event->time_delta = 1;
2493}
2494
2495static inline bool
2496rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2497                   struct ring_buffer_event *event)
2498{
2499        unsigned long addr = (unsigned long)event;
2500        unsigned long index;
2501
2502        index = rb_event_index(event);
2503        addr &= PAGE_MASK;
2504
2505        return cpu_buffer->commit_page->page == (void *)addr &&
2506                rb_commit_index(cpu_buffer) == index;
2507}
2508
2509static void
2510rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2511                      struct ring_buffer_event *event)
2512{
2513        u64 delta;
2514
2515        /*
2516         * The event first in the commit queue updates the
2517         * time stamp.
2518         */
2519        if (rb_event_is_commit(cpu_buffer, event)) {
2520                /*
2521                 * A commit event that is first on a page
2522                 * updates the write timestamp with the page stamp
2523                 */
2524                if (!rb_event_index(event))
2525                        cpu_buffer->write_stamp =
2526                                cpu_buffer->commit_page->page->time_stamp;
2527                else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2528                        delta = event->array[0];
2529                        delta <<= TS_SHIFT;
2530                        delta += event->time_delta;
2531                        cpu_buffer->write_stamp += delta;
2532                } else
2533                        cpu_buffer->write_stamp += event->time_delta;
2534        }
2535}
2536
2537static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2538                      struct ring_buffer_event *event)
2539{
2540        local_inc(&cpu_buffer->entries);
2541        rb_update_write_stamp(cpu_buffer, event);
2542        rb_end_commit(cpu_buffer);
2543}
2544
2545static __always_inline void
2546rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
2547{
2548        bool pagebusy;
2549
2550        if (buffer->irq_work.waiters_pending) {
2551                buffer->irq_work.waiters_pending = false;
2552                /* irq_work_queue() supplies it's own memory barriers */
2553                irq_work_queue(&buffer->irq_work.work);
2554        }
2555
2556        if (cpu_buffer->irq_work.waiters_pending) {
2557                cpu_buffer->irq_work.waiters_pending = false;
2558                /* irq_work_queue() supplies it's own memory barriers */
2559                irq_work_queue(&cpu_buffer->irq_work.work);
2560        }
2561
2562        pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
2563
2564        if (!pagebusy && cpu_buffer->irq_work.full_waiters_pending) {
2565                cpu_buffer->irq_work.wakeup_full = true;
2566                cpu_buffer->irq_work.full_waiters_pending = false;
2567                /* irq_work_queue() supplies it's own memory barriers */
2568                irq_work_queue(&cpu_buffer->irq_work.work);
2569        }
2570}
2571
2572/*
2573 * The lock and unlock are done within a preempt disable section.
2574 * The current_context per_cpu variable can only be modified
2575 * by the current task between lock and unlock. But it can
2576 * be modified more than once via an interrupt. To pass this
2577 * information from the lock to the unlock without having to
2578 * access the 'in_interrupt()' functions again (which do show
2579 * a bit of overhead in something as critical as function tracing,
2580 * we use a bitmask trick.
2581 *
2582 *  bit 0 =  NMI context
2583 *  bit 1 =  IRQ context
2584 *  bit 2 =  SoftIRQ context
2585 *  bit 3 =  normal context.
2586 *
2587 * This works because this is the order of contexts that can
2588 * preempt other contexts. A SoftIRQ never preempts an IRQ
2589 * context.
2590 *
2591 * When the context is determined, the corresponding bit is
2592 * checked and set (if it was set, then a recursion of that context
2593 * happened).
2594 *
2595 * On unlock, we need to clear this bit. To do so, just subtract
2596 * 1 from the current_context and AND it to itself.
2597 *
2598 * (binary)
2599 *  101 - 1 = 100
2600 *  101 & 100 = 100 (clearing bit zero)
2601 *
2602 *  1010 - 1 = 1001
2603 *  1010 & 1001 = 1000 (clearing bit 1)
2604 *
2605 * The least significant bit can be cleared this way, and it
2606 * just so happens that it is the same bit corresponding to
2607 * the current context.
2608 */
2609
2610static __always_inline int
2611trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
2612{
2613        unsigned int val = cpu_buffer->current_context;
2614        int bit;
2615
2616        if (in_interrupt()) {
2617                if (in_nmi())
2618                        bit = RB_CTX_NMI;
2619                else if (in_irq())
2620                        bit = RB_CTX_IRQ;
2621                else
2622                        bit = RB_CTX_SOFTIRQ;
2623        } else
2624                bit = RB_CTX_NORMAL;
2625
2626        if (unlikely(val & (1 << bit)))
2627                return 1;
2628
2629        val |= (1 << bit);
2630        cpu_buffer->current_context = val;
2631
2632        return 0;
2633}
2634
2635static __always_inline void
2636trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
2637{
2638        cpu_buffer->current_context &= cpu_buffer->current_context - 1;
2639}
2640
2641/**
2642 * ring_buffer_unlock_commit - commit a reserved
2643 * @buffer: The buffer to commit to
2644 * @event: The event pointer to commit.
2645 *
2646 * This commits the data to the ring buffer, and releases any locks held.
2647 *
2648 * Must be paired with ring_buffer_lock_reserve.
2649 */
2650int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2651                              struct ring_buffer_event *event)
2652{
2653        struct ring_buffer_per_cpu *cpu_buffer;
2654        int cpu = raw_smp_processor_id();
2655
2656        cpu_buffer = buffer->buffers[cpu];
2657
2658        rb_commit(cpu_buffer, event);
2659
2660        rb_wakeups(buffer, cpu_buffer);
2661
2662        trace_recursive_unlock(cpu_buffer);
2663
2664        preempt_enable_notrace();
2665
2666        return 0;
2667}
2668EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2669
2670static noinline void
2671rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2672                    struct rb_event_info *info)
2673{
2674        WARN_ONCE(info->delta > (1ULL << 59),
2675                  KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2676                  (unsigned long long)info->delta,
2677                  (unsigned long long)info->ts,
2678                  (unsigned long long)cpu_buffer->write_stamp,
2679                  sched_clock_stable() ? "" :
2680                  "If you just came from a suspend/resume,\n"
2681                  "please switch to the trace global clock:\n"
2682                  "  echo global > /sys/kernel/debug/tracing/trace_clock\n");
2683        info->add_timestamp = 1;
2684}
2685
2686static struct ring_buffer_event *
2687__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2688                  struct rb_event_info *info)
2689{
2690        struct ring_buffer_event *event;
2691        struct buffer_page *tail_page;
2692        unsigned long tail, write;
2693
2694        /*
2695         * If the time delta since the last event is too big to
2696         * hold in the time field of the event, then we append a
2697         * TIME EXTEND event ahead of the data event.
2698         */
2699        if (unlikely(info->add_timestamp))
2700                info->length += RB_LEN_TIME_EXTEND;
2701
2702        tail_page = info->tail_page = cpu_buffer->tail_page;
2703        write = local_add_return(info->length, &tail_page->write);
2704
2705        /* set write to only the index of the write */
2706        write &= RB_WRITE_MASK;
2707        tail = write - info->length;
2708
2709        /*
2710         * If this is the first commit on the page, then it has the same
2711         * timestamp as the page itself.
2712         */
2713        if (!tail)
2714                info->delta = 0;
2715
2716        /* See if we shot pass the end of this buffer page */
2717        if (unlikely(write > BUF_PAGE_SIZE))
2718                return rb_move_tail(cpu_buffer, tail, info);
2719
2720        /* We reserved something on the buffer */
2721
2722        event = __rb_page_index(tail_page, tail);
2723        kmemcheck_annotate_bitfield(event, bitfield);
2724        rb_update_event(cpu_buffer, event, info);
2725
2726        local_inc(&tail_page->entries);
2727
2728        /*
2729         * If this is the first commit on the page, then update
2730         * its timestamp.
2731         */
2732        if (!tail)
2733                tail_page->page->time_stamp = info->ts;
2734
2735        /* account for these added bytes */
2736        local_add(info->length, &cpu_buffer->entries_bytes);
2737
2738        return event;
2739}
2740
2741static struct ring_buffer_event *
2742rb_reserve_next_event(struct ring_buffer *buffer,
2743                      struct ring_buffer_per_cpu *cpu_buffer,
2744                      unsigned long length)
2745{
2746        struct ring_buffer_event *event;
2747        struct rb_event_info info;
2748        int nr_loops = 0;
2749        u64 diff;
2750
2751        rb_start_commit(cpu_buffer);
2752
2753#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2754        /*
2755         * Due to the ability to swap a cpu buffer from a buffer
2756         * it is possible it was swapped before we committed.
2757         * (committing stops a swap). We check for it here and
2758         * if it happened, we have to fail the write.
2759         */
2760        barrier();
2761        if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
2762                local_dec(&cpu_buffer->committing);
2763                local_dec(&cpu_buffer->commits);
2764                return NULL;
2765        }
2766#endif
2767
2768        info.length = rb_calculate_event_length(length);
2769 again:
2770        info.add_timestamp = 0;
2771        info.delta = 0;
2772
2773        /*
2774         * We allow for interrupts to reenter here and do a trace.
2775         * If one does, it will cause this original code to loop
2776         * back here. Even with heavy interrupts happening, this
2777         * should only happen a few times in a row. If this happens
2778         * 1000 times in a row, there must be either an interrupt
2779         * storm or we have something buggy.
2780         * Bail!
2781         */
2782        if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2783                goto out_fail;
2784
2785        info.ts = rb_time_stamp(cpu_buffer->buffer);
2786        diff = info.ts - cpu_buffer->write_stamp;
2787
2788        /* make sure this diff is calculated here */
2789        barrier();
2790
2791        /* Did the write stamp get updated already? */
2792        if (likely(info.ts >= cpu_buffer->write_stamp)) {
2793                info.delta = diff;
2794                if (unlikely(test_time_stamp(info.delta)))
2795                        rb_handle_timestamp(cpu_buffer, &info);
2796        }
2797
2798        event = __rb_reserve_next(cpu_buffer, &info);
2799
2800        if (unlikely(PTR_ERR(event) == -EAGAIN)) {
2801                if (info.add_timestamp)
2802                        info.length -= RB_LEN_TIME_EXTEND;
2803                goto again;
2804        }
2805
2806        if (!event)
2807                goto out_fail;
2808
2809        return event;
2810
2811 out_fail:
2812        rb_end_commit(cpu_buffer);
2813        return NULL;
2814}
2815
2816/**
2817 * ring_buffer_lock_reserve - reserve a part of the buffer
2818 * @buffer: the ring buffer to reserve from
2819 * @length: the length of the data to reserve (excluding event header)
2820 *
2821 * Returns a reseverd event on the ring buffer to copy directly to.
2822 * The user of this interface will need to get the body to write into
2823 * and can use the ring_buffer_event_data() interface.
2824 *
2825 * The length is the length of the data needed, not the event length
2826 * which also includes the event header.
2827 *
2828 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2829 * If NULL is returned, then nothing has been allocated or locked.
2830 */
2831struct ring_buffer_event *
2832ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2833{
2834        struct ring_buffer_per_cpu *cpu_buffer;
2835        struct ring_buffer_event *event;
2836        int cpu;
2837
2838        /* If we are tracing schedule, we don't want to recurse */
2839        preempt_disable_notrace();
2840
2841        if (unlikely(atomic_read(&buffer->record_disabled)))
2842                goto out;
2843
2844        cpu = raw_smp_processor_id();
2845
2846        if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
2847                goto out;
2848
2849        cpu_buffer = buffer->buffers[cpu];
2850
2851        if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
2852                goto out;
2853
2854        if (unlikely(length > BUF_MAX_DATA_SIZE))
2855                goto out;
2856
2857        if (unlikely(trace_recursive_lock(cpu_buffer)))
2858                goto out;
2859
2860        event = rb_reserve_next_event(buffer, cpu_buffer, length);
2861        if (!event)
2862                goto out_unlock;
2863
2864        return event;
2865
2866 out_unlock:
2867        trace_recursive_unlock(cpu_buffer);
2868 out:
2869        preempt_enable_notrace();
2870        return NULL;
2871}
2872EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
2873
2874/*
2875 * Decrement the entries to the page that an event is on.
2876 * The event does not even need to exist, only the pointer
2877 * to the page it is on. This may only be called before the commit
2878 * takes place.
2879 */
2880static inline void
2881rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
2882                   struct ring_buffer_event *event)
2883{
2884        unsigned long addr = (unsigned long)event;
2885        struct buffer_page *bpage = cpu_buffer->commit_page;
2886        struct buffer_page *start;
2887
2888        addr &= PAGE_MASK;
2889
2890        /* Do the likely case first */
2891        if (likely(bpage->page == (void *)addr)) {
2892                local_dec(&bpage->entries);
2893                return;
2894        }
2895
2896        /*
2897         * Because the commit page may be on the reader page we
2898         * start with the next page and check the end loop there.
2899         */
2900        rb_inc_page(cpu_buffer, &bpage);
2901        start = bpage;
2902        do {
2903                if (bpage->page == (void *)addr) {
2904                        local_dec(&bpage->entries);
2905                        return;
2906                }
2907                rb_inc_page(cpu_buffer, &bpage);
2908        } while (bpage != start);
2909
2910        /* commit not part of this buffer?? */
2911        RB_WARN_ON(cpu_buffer, 1);
2912}
2913
2914/**
2915 * ring_buffer_commit_discard - discard an event that has not been committed
2916 * @buffer: the ring buffer
2917 * @event: non committed event to discard
2918 *
2919 * Sometimes an event that is in the ring buffer needs to be ignored.
2920 * This function lets the user discard an event in the ring buffer
2921 * and then that event will not be read later.
2922 *
2923 * This function only works if it is called before the the item has been
2924 * committed. It will try to free the event from the ring buffer
2925 * if another event has not been added behind it.
2926 *
2927 * If another event has been added behind it, it will set the event
2928 * up as discarded, and perform the commit.
2929 *
2930 * If this function is called, do not call ring_buffer_unlock_commit on
2931 * the event.
2932 */
2933void ring_buffer_discard_commit(struct ring_buffer *buffer,
2934                                struct ring_buffer_event *event)
2935{
2936        struct ring_buffer_per_cpu *cpu_buffer;
2937        int cpu;
2938
2939        /* The event is discarded regardless */
2940        rb_event_discard(event);
2941
2942        cpu = smp_processor_id();
2943        cpu_buffer = buffer->buffers[cpu];
2944
2945        /*
2946         * This must only be called if the event has not been
2947         * committed yet. Thus we can assume that preemption
2948         * is still disabled.
2949         */
2950        RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
2951
2952        rb_decrement_entry(cpu_buffer, event);
2953        if (rb_try_to_discard(cpu_buffer, event))
2954                goto out;
2955
2956        /*
2957         * The commit is still visible by the reader, so we
2958         * must still update the timestamp.
2959         */
2960        rb_update_write_stamp(cpu_buffer, event);
2961 out:
2962        rb_end_commit(cpu_buffer);
2963
2964        trace_recursive_unlock(cpu_buffer);
2965
2966        preempt_enable_notrace();
2967
2968}
2969EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
2970
2971/**
2972 * ring_buffer_write - write data to the buffer without reserving
2973 * @buffer: The ring buffer to write to.
2974 * @length: The length of the data being written (excluding the event header)
2975 * @data: The data to write to the buffer.
2976 *
2977 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
2978 * one function. If you already have the data to write to the buffer, it
2979 * may be easier to simply call this function.
2980 *
2981 * Note, like ring_buffer_lock_reserve, the length is the length of the data
2982 * and not the length of the event which would hold the header.
2983 */
2984int ring_buffer_write(struct ring_buffer *buffer,
2985                      unsigned long length,
2986                      void *data)
2987{
2988        struct ring_buffer_per_cpu *cpu_buffer;
2989        struct ring_buffer_event *event;
2990        void *body;
2991        int ret = -EBUSY;
2992        int cpu;
2993
2994        preempt_disable_notrace();
2995
2996        if (atomic_read(&buffer->record_disabled))
2997                goto out;
2998
2999        cpu = raw_smp_processor_id();
3000
3001        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3002                goto out;
3003
3004        cpu_buffer = buffer->buffers[cpu];
3005
3006        if (atomic_read(&cpu_buffer->record_disabled))
3007                goto out;
3008
3009        if (length > BUF_MAX_DATA_SIZE)
3010                goto out;
3011
3012        if (unlikely(trace_recursive_lock(cpu_buffer)))
3013                goto out;
3014
3015        event = rb_reserve_next_event(buffer, cpu_buffer, length);
3016        if (!event)
3017                goto out_unlock;
3018
3019        body = rb_event_data(event);
3020
3021        memcpy(body, data, length);
3022
3023        rb_commit(cpu_buffer, event);
3024
3025        rb_wakeups(buffer, cpu_buffer);
3026
3027        ret = 0;
3028
3029 out_unlock:
3030        trace_recursive_unlock(cpu_buffer);
3031
3032 out:
3033        preempt_enable_notrace();
3034
3035        return ret;
3036}
3037EXPORT_SYMBOL_GPL(ring_buffer_write);
3038
3039static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3040{
3041        struct buffer_page *reader = cpu_buffer->reader_page;
3042        struct buffer_page *head = rb_set_head_page(cpu_buffer);
3043        struct buffer_page *commit = cpu_buffer->commit_page;
3044
3045        /* In case of error, head will be NULL */
3046        if (unlikely(!head))
3047                return true;
3048
3049        return reader->read == rb_page_commit(reader) &&
3050                (commit == reader ||
3051                 (commit == head &&
3052                  head->read == rb_page_commit(commit)));
3053}
3054
3055/**
3056 * ring_buffer_record_disable - stop all writes into the buffer
3057 * @buffer: The ring buffer to stop writes to.
3058 *
3059 * This prevents all writes to the buffer. Any attempt to write
3060 * to the buffer after this will fail and return NULL.
3061 *
3062 * The caller should call synchronize_sched() after this.
3063 */
3064void ring_buffer_record_disable(struct ring_buffer *buffer)
3065{
3066        atomic_inc(&buffer->record_disabled);
3067}
3068EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3069
3070/**
3071 * ring_buffer_record_enable - enable writes to the buffer
3072 * @buffer: The ring buffer to enable writes
3073 *
3074 * Note, multiple disables will need the same number of enables
3075 * to truly enable the writing (much like preempt_disable).
3076 */
3077void ring_buffer_record_enable(struct ring_buffer *buffer)
3078{
3079        atomic_dec(&buffer->record_disabled);
3080}
3081EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3082
3083/**
3084 * ring_buffer_record_off - stop all writes into the buffer
3085 * @buffer: The ring buffer to stop writes to.
3086 *
3087 * This prevents all writes to the buffer. Any attempt to write
3088 * to the buffer after this will fail and return NULL.
3089 *
3090 * This is different than ring_buffer_record_disable() as
3091 * it works like an on/off switch, where as the disable() version
3092 * must be paired with a enable().
3093 */
3094void ring_buffer_record_off(struct ring_buffer *buffer)
3095{
3096        unsigned int rd;
3097        unsigned int new_rd;
3098
3099        do {
3100                rd = atomic_read(&buffer->record_disabled);
3101                new_rd = rd | RB_BUFFER_OFF;
3102        } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3103}
3104EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3105
3106/**
3107 * ring_buffer_record_on - restart writes into the buffer
3108 * @buffer: The ring buffer to start writes to.
3109 *
3110 * This enables all writes to the buffer that was disabled by
3111 * ring_buffer_record_off().
3112 *
3113 * This is different than ring_buffer_record_enable() as
3114 * it works like an on/off switch, where as the enable() version
3115 * must be paired with a disable().
3116 */
3117void ring_buffer_record_on(struct ring_buffer *buffer)
3118{
3119        unsigned int rd;
3120        unsigned int new_rd;
3121
3122        do {
3123                rd = atomic_read(&buffer->record_disabled);
3124                new_rd = rd & ~RB_BUFFER_OFF;
3125        } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3126}
3127EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3128
3129/**
3130 * ring_buffer_record_is_on - return true if the ring buffer can write
3131 * @buffer: The ring buffer to see if write is enabled
3132 *
3133 * Returns true if the ring buffer is in a state that it accepts writes.
3134 */
3135int ring_buffer_record_is_on(struct ring_buffer *buffer)
3136{
3137        return !atomic_read(&buffer->record_disabled);
3138}
3139
3140/**
3141 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3142 * @buffer: The ring buffer to stop writes to.
3143 * @cpu: The CPU buffer to stop
3144 *
3145 * This prevents all writes to the buffer. Any attempt to write
3146 * to the buffer after this will fail and return NULL.
3147 *
3148 * The caller should call synchronize_sched() after this.
3149 */
3150void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
3151{
3152        struct ring_buffer_per_cpu *cpu_buffer;
3153
3154        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3155                return;
3156
3157        cpu_buffer = buffer->buffers[cpu];
3158        atomic_inc(&cpu_buffer->record_disabled);
3159}
3160EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
3161
3162/**
3163 * ring_buffer_record_enable_cpu - enable writes to the buffer
3164 * @buffer: The ring buffer to enable writes
3165 * @cpu: The CPU to enable.
3166 *
3167 * Note, multiple disables will need the same number of enables
3168 * to truly enable the writing (much like preempt_disable).
3169 */
3170void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
3171{
3172        struct ring_buffer_per_cpu *cpu_buffer;
3173
3174        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3175                return;
3176
3177        cpu_buffer = buffer->buffers[cpu];
3178        atomic_dec(&cpu_buffer->record_disabled);
3179}
3180EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
3181
3182/*
3183 * The total entries in the ring buffer is the running counter
3184 * of entries entered into the ring buffer, minus the sum of
3185 * the entries read from the ring buffer and the number of
3186 * entries that were overwritten.
3187 */
3188static inline unsigned long
3189rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
3190{
3191        return local_read(&cpu_buffer->entries) -
3192                (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
3193}
3194
3195/**
3196 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
3197 * @buffer: The ring buffer
3198 * @cpu: The per CPU buffer to read from.
3199 */
3200u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
3201{
3202        unsigned long flags;
3203        struct ring_buffer_per_cpu *cpu_buffer;
3204        struct buffer_page *bpage;
3205        u64 ret = 0;
3206
3207        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3208                return 0;
3209
3210        cpu_buffer = buffer->buffers[cpu];
3211        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3212        /*
3213         * if the tail is on reader_page, oldest time stamp is on the reader
3214         * page
3215         */
3216        if (cpu_buffer->tail_page == cpu_buffer->reader_page)
3217                bpage = cpu_buffer->reader_page;
3218        else
3219                bpage = rb_set_head_page(cpu_buffer);
3220        if (bpage)
3221                ret = bpage->page->time_stamp;
3222        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3223
3224        return ret;
3225}
3226EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
3227
3228/**
3229 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
3230 * @buffer: The ring buffer
3231 * @cpu: The per CPU buffer to read from.
3232 */
3233unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
3234{
3235        struct ring_buffer_per_cpu *cpu_buffer;
3236        unsigned long ret;
3237
3238        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3239                return 0;
3240
3241        cpu_buffer = buffer->buffers[cpu];
3242        ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
3243
3244        return ret;
3245}
3246EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
3247
3248/**
3249 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
3250 * @buffer: The ring buffer
3251 * @cpu: The per CPU buffer to get the entries from.
3252 */
3253unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
3254{
3255        struct ring_buffer_per_cpu *cpu_buffer;
3256
3257        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3258                return 0;
3259
3260        cpu_buffer = buffer->buffers[cpu];
3261
3262        return rb_num_of_entries(cpu_buffer);
3263}
3264EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
3265
3266/**
3267 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
3268 * buffer wrapping around (only if RB_FL_OVERWRITE is on).
3269 * @buffer: The ring buffer
3270 * @cpu: The per CPU buffer to get the number of overruns from
3271 */
3272unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
3273{
3274        struct ring_buffer_per_cpu *cpu_buffer;
3275        unsigned long ret;
3276
3277        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3278                return 0;
3279
3280        cpu_buffer = buffer->buffers[cpu];
3281        ret = local_read(&cpu_buffer->overrun);
3282
3283        return ret;
3284}
3285EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3286
3287/**
3288 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
3289 * commits failing due to the buffer wrapping around while there are uncommitted
3290 * events, such as during an interrupt storm.
3291 * @buffer: The ring buffer
3292 * @cpu: The per CPU buffer to get the number of overruns from
3293 */
3294unsigned long
3295ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3296{
3297        struct ring_buffer_per_cpu *cpu_buffer;
3298        unsigned long ret;
3299
3300        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3301                return 0;
3302
3303        cpu_buffer = buffer->buffers[cpu];
3304        ret = local_read(&cpu_buffer->commit_overrun);
3305
3306        return ret;
3307}
3308EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3309
3310/**
3311 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
3312 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
3313 * @buffer: The ring buffer
3314 * @cpu: The per CPU buffer to get the number of overruns from
3315 */
3316unsigned long
3317ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
3318{
3319        struct ring_buffer_per_cpu *cpu_buffer;
3320        unsigned long ret;
3321
3322        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3323                return 0;
3324
3325        cpu_buffer = buffer->buffers[cpu];
3326        ret = local_read(&cpu_buffer->dropped_events);
3327
3328        return ret;
3329}
3330EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
3331
3332/**
3333 * ring_buffer_read_events_cpu - get the number of events successfully read
3334 * @buffer: The ring buffer
3335 * @cpu: The per CPU buffer to get the number of events read
3336 */
3337unsigned long
3338ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
3339{
3340        struct ring_buffer_per_cpu *cpu_buffer;
3341
3342        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3343                return 0;
3344
3345        cpu_buffer = buffer->buffers[cpu];
3346        return cpu_buffer->read;
3347}
3348EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
3349
3350/**
3351 * ring_buffer_entries - get the number of entries in a buffer
3352 * @buffer: The ring buffer
3353 *
3354 * Returns the total number of entries in the ring buffer
3355 * (all CPU entries)
3356 */
3357unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3358{
3359        struct ring_buffer_per_cpu *cpu_buffer;
3360        unsigned long entries = 0;
3361        int cpu;
3362
3363        /* if you care about this being correct, lock the buffer */
3364        for_each_buffer_cpu(buffer, cpu) {
3365                cpu_buffer = buffer->buffers[cpu];
3366                entries += rb_num_of_entries(cpu_buffer);
3367        }
3368
3369        return entries;
3370}
3371EXPORT_SYMBOL_GPL(ring_buffer_entries);
3372
3373/**
3374 * ring_buffer_overruns - get the number of overruns in buffer
3375 * @buffer: The ring buffer
3376 *
3377 * Returns the total number of overruns in the ring buffer
3378 * (all CPU entries)
3379 */
3380unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3381{
3382        struct ring_buffer_per_cpu *cpu_buffer;
3383        unsigned long overruns = 0;
3384        int cpu;
3385
3386        /* if you care about this being correct, lock the buffer */
3387        for_each_buffer_cpu(buffer, cpu) {
3388                cpu_buffer = buffer->buffers[cpu];
3389                overruns += local_read(&cpu_buffer->overrun);
3390        }
3391
3392        return overruns;
3393}
3394EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3395
3396static void rb_iter_reset(struct ring_buffer_iter *iter)
3397{
3398        struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3399
3400        /* Iterator usage is expected to have record disabled */
3401        iter->head_page = cpu_buffer->reader_page;
3402        iter->head = cpu_buffer->reader_page->read;
3403
3404        iter->cache_reader_page = iter->head_page;
3405        iter->cache_read = cpu_buffer->read;
3406
3407        if (iter->head)
3408                iter->read_stamp = cpu_buffer->read_stamp;
3409        else
3410                iter->read_stamp = iter->head_page->page->time_stamp;
3411}
3412
3413/**
3414 * ring_buffer_iter_reset - reset an iterator
3415 * @iter: The iterator to reset
3416 *
3417 * Resets the iterator, so that it will start from the beginning
3418 * again.
3419 */
3420void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3421{
3422        struct ring_buffer_per_cpu *cpu_buffer;
3423        unsigned long flags;
3424
3425        if (!iter)
3426                return;
3427
3428        cpu_buffer = iter->cpu_buffer;
3429
3430        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3431        rb_iter_reset(iter);
3432        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3433}
3434EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3435
3436/**
3437 * ring_buffer_iter_empty - check if an iterator has no more to read
3438 * @iter: The iterator to check
3439 */
3440int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3441{
3442        struct ring_buffer_per_cpu *cpu_buffer;
3443
3444        cpu_buffer = iter->cpu_buffer;
3445
3446        return iter->head_page == cpu_buffer->commit_page &&
3447                iter->head == rb_commit_index(cpu_buffer);
3448}
3449EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3450
3451static void
3452rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3453                     struct ring_buffer_event *event)
3454{
3455        u64 delta;
3456
3457        switch (event->type_len) {
3458        case RINGBUF_TYPE_PADDING:
3459                return;
3460
3461        case RINGBUF_TYPE_TIME_EXTEND:
3462                delta = event->array[0];
3463                delta <<= TS_SHIFT;
3464                delta += event->time_delta;
3465                cpu_buffer->read_stamp += delta;
3466                return;
3467
3468        case RINGBUF_TYPE_TIME_STAMP:
3469                /* FIXME: not implemented */
3470                return;
3471
3472        case RINGBUF_TYPE_DATA:
3473                cpu_buffer->read_stamp += event->time_delta;
3474                return;
3475
3476        default:
3477                BUG();
3478        }
3479        return;
3480}
3481
3482static void
3483rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3484                          struct ring_buffer_event *event)
3485{
3486        u64 delta;
3487
3488        switch (event->type_len) {
3489        case RINGBUF_TYPE_PADDING:
3490                return;
3491
3492        case RINGBUF_TYPE_TIME_EXTEND:
3493                delta = event->array[0];
3494                delta <<= TS_SHIFT;
3495                delta += event->time_delta;
3496                iter->read_stamp += delta;
3497                return;
3498
3499        case RINGBUF_TYPE_TIME_STAMP:
3500                /* FIXME: not implemented */
3501                return;
3502
3503        case RINGBUF_TYPE_DATA:
3504                iter->read_stamp += event->time_delta;
3505                return;
3506
3507        default:
3508                BUG();
3509        }
3510        return;
3511}
3512
3513static struct buffer_page *
3514rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3515{
3516        struct buffer_page *reader = NULL;
3517        unsigned long overwrite;
3518        unsigned long flags;
3519        int nr_loops = 0;
3520        int ret;
3521
3522        local_irq_save(flags);
3523        arch_spin_lock(&cpu_buffer->lock);
3524
3525 again:
3526        /*
3527         * This should normally only loop twice. But because the
3528         * start of the reader inserts an empty page, it causes
3529         * a case where we will loop three times. There should be no
3530         * reason to loop four times (that I know of).
3531         */
3532        if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3533                reader = NULL;
3534                goto out;
3535        }
3536
3537        reader = cpu_buffer->reader_page;
3538
3539        /* If there's more to read, return this page */
3540        if (cpu_buffer->reader_page->read < rb_page_size(reader))
3541                goto out;
3542
3543        /* Never should we have an index greater than the size */
3544        if (RB_WARN_ON(cpu_buffer,
3545                       cpu_buffer->reader_page->read > rb_page_size(reader)))
3546                goto out;
3547
3548        /* check if we caught up to the tail */
3549        reader = NULL;
3550        if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3551                goto out;
3552
3553        /* Don't bother swapping if the ring buffer is empty */
3554        if (rb_num_of_entries(cpu_buffer) == 0)
3555                goto out;
3556
3557        /*
3558         * Reset the reader page to size zero.
3559         */
3560        local_set(&cpu_buffer->reader_page->write, 0);
3561        local_set(&cpu_buffer->reader_page->entries, 0);
3562        local_set(&cpu_buffer->reader_page->page->commit, 0);
3563        cpu_buffer->reader_page->real_end = 0;
3564
3565 spin:
3566        /*
3567         * Splice the empty reader page into the list around the head.
3568         */
3569        reader = rb_set_head_page(cpu_buffer);
3570        if (!reader)
3571                goto out;
3572        cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3573        cpu_buffer->reader_page->list.prev = reader->list.prev;
3574
3575        /*
3576         * cpu_buffer->pages just needs to point to the buffer, it
3577         *  has no specific buffer page to point to. Lets move it out
3578         *  of our way so we don't accidentally swap it.
3579         */
3580        cpu_buffer->pages = reader->list.prev;
3581
3582        /* The reader page will be pointing to the new head */
3583        rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3584
3585        /*
3586         * We want to make sure we read the overruns after we set up our
3587         * pointers to the next object. The writer side does a
3588         * cmpxchg to cross pages which acts as the mb on the writer
3589         * side. Note, the reader will constantly fail the swap
3590         * while the writer is updating the pointers, so this
3591         * guarantees that the overwrite recorded here is the one we
3592         * want to compare with the last_overrun.
3593         */
3594        smp_mb();
3595        overwrite = local_read(&(cpu_buffer->overrun));
3596
3597        /*
3598         * Here's the tricky part.
3599         *
3600         * We need to move the pointer past the header page.
3601         * But we can only do that if a writer is not currently
3602         * moving it. The page before the header page has the
3603         * flag bit '1' set if it is pointing to the page we want.
3604         * but if the writer is in the process of moving it
3605         * than it will be '2' or already moved '0'.
3606         */
3607
3608        ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3609
3610        /*
3611         * If we did not convert it, then we must try again.
3612         */
3613        if (!ret)
3614                goto spin;
3615
3616        /*
3617         * Yeah! We succeeded in replacing the page.
3618         *
3619         * Now make the new head point back to the reader page.
3620         */
3621        rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3622        rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3623
3624        /* Finally update the reader page to the new head */
3625        cpu_buffer->reader_page = reader;
3626        cpu_buffer->reader_page->read = 0;
3627
3628        if (overwrite != cpu_buffer->last_overrun) {
3629                cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3630                cpu_buffer->last_overrun = overwrite;
3631        }
3632
3633        goto again;
3634
3635 out:
3636        /* Update the read_stamp on the first event */
3637        if (reader && reader->read == 0)
3638                cpu_buffer->read_stamp = reader->page->time_stamp;
3639
3640        arch_spin_unlock(&cpu_buffer->lock);
3641        local_irq_restore(flags);
3642
3643        return reader;
3644}
3645
3646static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3647{
3648        struct ring_buffer_event *event;
3649        struct buffer_page *reader;
3650        unsigned length;
3651
3652        reader = rb_get_reader_page(cpu_buffer);
3653
3654        /* This function should not be called when buffer is empty */
3655        if (RB_WARN_ON(cpu_buffer, !reader))
3656                return;
3657
3658        event = rb_reader_event(cpu_buffer);
3659
3660        if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3661                cpu_buffer->read++;
3662
3663        rb_update_read_stamp(cpu_buffer, event);
3664
3665        length = rb_event_length(event);
3666        cpu_buffer->reader_page->read += length;
3667}
3668
3669static void rb_advance_iter(struct ring_buffer_iter *iter)
3670{
3671        struct ring_buffer_per_cpu *cpu_buffer;
3672        struct ring_buffer_event *event;
3673        unsigned length;
3674
3675        cpu_buffer = iter->cpu_buffer;
3676
3677        /*
3678         * Check if we are at the end of the buffer.
3679         */
3680        if (iter->head >= rb_page_size(iter->head_page)) {
3681                /* discarded commits can make the page empty */
3682                if (iter->head_page == cpu_buffer->commit_page)
3683                        return;
3684                rb_inc_iter(iter);
3685                return;
3686        }
3687
3688        event = rb_iter_head_event(iter);
3689
3690        length = rb_event_length(event);
3691
3692        /*
3693         * This should not be called to advance the header if we are
3694         * at the tail of the buffer.
3695         */
3696        if (RB_WARN_ON(cpu_buffer,
3697                       (iter->head_page == cpu_buffer->commit_page) &&
3698                       (iter->head + length > rb_commit_index(cpu_buffer))))
3699                return;
3700
3701        rb_update_iter_read_stamp(iter, event);
3702
3703        iter->head += length;
3704
3705        /* check for end of page padding */
3706        if ((iter->head >= rb_page_size(iter->head_page)) &&
3707            (iter->head_page != cpu_buffer->commit_page))
3708                rb_inc_iter(iter);
3709}
3710
3711static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3712{
3713        return cpu_buffer->lost_events;
3714}
3715
3716static struct ring_buffer_event *
3717rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3718               unsigned long *lost_events)
3719{
3720        struct ring_buffer_event *event;
3721        struct buffer_page *reader;
3722        int nr_loops = 0;
3723
3724 again:
3725        /*
3726         * We repeat when a time extend is encountered.
3727         * Since the time extend is always attached to a data event,
3728         * we should never loop more than once.
3729         * (We never hit the following condition more than twice).
3730         */
3731        if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3732                return NULL;
3733
3734        reader = rb_get_reader_page(cpu_buffer);
3735        if (!reader)
3736                return NULL;
3737
3738        event = rb_reader_event(cpu_buffer);
3739
3740        switch (event->type_len) {
3741        case RINGBUF_TYPE_PADDING:
3742                if (rb_null_event(event))
3743                        RB_WARN_ON(cpu_buffer, 1);
3744                /*
3745                 * Because the writer could be discarding every
3746                 * event it creates (which would probably be bad)
3747                 * if we were to go back to "again" then we may never
3748                 * catch up, and will trigger the warn on, or lock
3749                 * the box. Return the padding, and we will release
3750                 * the current locks, and try again.
3751                 */
3752                return event;
3753
3754        case RINGBUF_TYPE_TIME_EXTEND:
3755                /* Internal data, OK to advance */
3756                rb_advance_reader(cpu_buffer);
3757                goto again;
3758
3759        case RINGBUF_TYPE_TIME_STAMP:
3760                /* FIXME: not implemented */
3761                rb_advance_reader(cpu_buffer);
3762                goto again;
3763
3764        case RINGBUF_TYPE_DATA:
3765                if (ts) {
3766                        *ts = cpu_buffer->read_stamp + event->time_delta;
3767                        ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3768                                                         cpu_buffer->cpu, ts);
3769                }
3770                if (lost_events)
3771                        *lost_events = rb_lost_events(cpu_buffer);
3772                return event;
3773
3774        default:
3775                BUG();
3776        }
3777
3778        return NULL;
3779}
3780EXPORT_SYMBOL_GPL(ring_buffer_peek);
3781
3782static struct ring_buffer_event *
3783rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3784{
3785        struct ring_buffer *buffer;
3786        struct ring_buffer_per_cpu *cpu_buffer;
3787        struct ring_buffer_event *event;
3788        int nr_loops = 0;
3789
3790        cpu_buffer = iter->cpu_buffer;
3791        buffer = cpu_buffer->buffer;
3792
3793        /*
3794         * Check if someone performed a consuming read to
3795         * the buffer. A consuming read invalidates the iterator
3796         * and we need to reset the iterator in this case.
3797         */
3798        if (unlikely(iter->cache_read != cpu_buffer->read ||
3799                     iter->cache_reader_page != cpu_buffer->reader_page))
3800                rb_iter_reset(iter);
3801
3802 again:
3803        if (ring_buffer_iter_empty(iter))
3804                return NULL;
3805
3806        /*
3807         * We repeat when a time extend is encountered or we hit
3808         * the end of the page. Since the time extend is always attached
3809         * to a data event, we should never loop more than three times.
3810         * Once for going to next page, once on time extend, and
3811         * finally once to get the event.
3812         * (We never hit the following condition more than thrice).
3813         */
3814        if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3))
3815                return NULL;
3816
3817        if (rb_per_cpu_empty(cpu_buffer))
3818                return NULL;
3819
3820        if (iter->head >= rb_page_size(iter->head_page)) {
3821                rb_inc_iter(iter);
3822                goto again;
3823        }
3824
3825        event = rb_iter_head_event(iter);
3826
3827        switch (event->type_len) {
3828        case RINGBUF_TYPE_PADDING:
3829                if (rb_null_event(event)) {
3830                        rb_inc_iter(iter);
3831                        goto again;
3832                }
3833                rb_advance_iter(iter);
3834                return event;
3835
3836        case RINGBUF_TYPE_TIME_EXTEND:
3837                /* Internal data, OK to advance */
3838                rb_advance_iter(iter);
3839                goto again;
3840
3841        case RINGBUF_TYPE_TIME_STAMP:
3842                /* FIXME: not implemented */
3843                rb_advance_iter(iter);
3844                goto again;
3845
3846        case RINGBUF_TYPE_DATA:
3847                if (ts) {
3848                        *ts = iter->read_stamp + event->time_delta;
3849                        ring_buffer_normalize_time_stamp(buffer,
3850                                                         cpu_buffer->cpu, ts);
3851                }
3852                return event;
3853
3854        default:
3855                BUG();
3856        }
3857
3858        return NULL;
3859}
3860EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
3861
3862static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
3863{
3864        if (likely(!in_nmi())) {
3865                raw_spin_lock(&cpu_buffer->reader_lock);
3866                return true;
3867        }
3868
3869        /*
3870         * If an NMI die dumps out the content of the ring buffer
3871         * trylock must be used to prevent a deadlock if the NMI
3872         * preempted a task that holds the ring buffer locks. If
3873         * we get the lock then all is fine, if not, then continue
3874         * to do the read, but this can corrupt the ring buffer,
3875         * so it must be permanently disabled from future writes.
3876         * Reading from NMI is a oneshot deal.
3877         */
3878        if (raw_spin_trylock(&cpu_buffer->reader_lock))
3879                return true;
3880
3881        /* Continue without locking, but disable the ring buffer */
3882        atomic_inc(&cpu_buffer->record_disabled);
3883        return false;
3884}
3885
3886static inline void
3887rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
3888{
3889        if (likely(locked))
3890                raw_spin_unlock(&cpu_buffer->reader_lock);
3891        return;
3892}
3893
3894/**
3895 * ring_buffer_peek - peek at the next event to be read
3896 * @buffer: The ring buffer to read
3897 * @cpu: The cpu to peak at
3898 * @ts: The timestamp counter of this event.
3899 * @lost_events: a variable to store if events were lost (may be NULL)
3900 *
3901 * This will return the event that will be read next, but does
3902 * not consume the data.
3903 */
3904struct ring_buffer_event *
3905ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
3906                 unsigned long *lost_events)
3907{
3908        struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3909        struct ring_buffer_event *event;
3910        unsigned long flags;
3911        bool dolock;
3912
3913        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3914                return NULL;
3915
3916 again:
3917        local_irq_save(flags);
3918        dolock = rb_reader_lock(cpu_buffer);
3919        event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3920        if (event && event->type_len == RINGBUF_TYPE_PADDING)
3921                rb_advance_reader(cpu_buffer);
3922        rb_reader_unlock(cpu_buffer, dolock);
3923        local_irq_restore(flags);
3924
3925        if (event && event->type_len == RINGBUF_TYPE_PADDING)
3926                goto again;
3927
3928        return event;
3929}
3930
3931/**
3932 * ring_buffer_iter_peek - peek at the next event to be read
3933 * @iter: The ring buffer iterator
3934 * @ts: The timestamp counter of this event.
3935 *
3936 * This will return the event that will be read next, but does
3937 * not increment the iterator.
3938 */
3939struct ring_buffer_event *
3940ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3941{
3942        struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3943        struct ring_buffer_event *event;
3944        unsigned long flags;
3945
3946 again:
3947        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3948        event = rb_iter_peek(iter, ts);
3949        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3950
3951        if (event && event->type_len == RINGBUF_TYPE_PADDING)
3952                goto again;
3953
3954        return event;
3955}
3956
3957/**
3958 * ring_buffer_consume - return an event and consume it
3959 * @buffer: The ring buffer to get the next event from
3960 * @cpu: the cpu to read the buffer from
3961 * @ts: a variable to store the timestamp (may be NULL)
3962 * @lost_events: a variable to store if events were lost (may be NULL)
3963 *
3964 * Returns the next event in the ring buffer, and that event is consumed.
3965 * Meaning, that sequential reads will keep returning a different event,
3966 * and eventually empty the ring buffer if the producer is slower.
3967 */
3968struct ring_buffer_event *
3969ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
3970                    unsigned long *lost_events)
3971{
3972        struct ring_buffer_per_cpu *cpu_buffer;
3973        struct ring_buffer_event *event = NULL;
3974        unsigned long flags;
3975        bool dolock;
3976
3977 again:
3978        /* might be called in atomic */
3979        preempt_disable();
3980
3981        if (!cpumask_test_cpu(cpu, buffer->cpumask))
3982                goto out;
3983
3984        cpu_buffer = buffer->buffers[cpu];
3985        local_irq_save(flags);
3986        dolock = rb_reader_lock(cpu_buffer);
3987
3988        event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3989        if (event) {
3990                cpu_buffer->lost_events = 0;
3991                rb_advance_reader(cpu_buffer);
3992        }
3993
3994        rb_reader_unlock(cpu_buffer, dolock);
3995        local_irq_restore(flags);
3996
3997 out:
3998        preempt_enable();
3999
4000        if (event && event->type_len == RINGBUF_TYPE_PADDING)
4001                goto again;
4002
4003        return event;
4004}
4005EXPORT_SYMBOL_GPL(ring_buffer_consume);
4006
4007/**
4008 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
4009 * @buffer: The ring buffer to read from
4010 * @cpu: The cpu buffer to iterate over
4011 *
4012 * This performs the initial preparations necessary to iterate
4013 * through the buffer.  Memory is allocated, buffer recording
4014 * is disabled, and the iterator pointer is returned to the caller.
4015 *
4016 * Disabling buffer recordng prevents the reading from being
4017 * corrupted. This is not a consuming read, so a producer is not
4018 * expected.
4019 *
4020 * After a sequence of ring_buffer_read_prepare calls, the user is
4021 * expected to make at least one call to ring_buffer_read_prepare_sync.
4022 * Afterwards, ring_buffer_read_start is invoked to get things going
4023 * for real.
4024 *
4025 * This overall must be paired with ring_buffer_read_finish.
4026 */
4027struct ring_buffer_iter *
4028ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
4029{
4030        struct ring_buffer_per_cpu *cpu_buffer;
4031        struct ring_buffer_iter *iter;
4032
4033        if (!cpumask_test_cpu(cpu, buffer->cpumask))
4034                return NULL;
4035
4036        iter = kmalloc(sizeof(*iter), GFP_KERNEL);
4037        if (!iter)
4038                return NULL;
4039
4040        cpu_buffer = buffer->buffers[cpu];
4041
4042        iter->cpu_buffer = cpu_buffer;
4043
4044        atomic_inc(&buffer->resize_disabled);
4045        atomic_inc(&cpu_buffer->record_disabled);
4046
4047        return iter;
4048}
4049EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
4050
4051/**
4052 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
4053 *
4054 * All previously invoked ring_buffer_read_prepare calls to prepare
4055 * iterators will be synchronized.  Afterwards, read_buffer_read_start
4056 * calls on those iterators are allowed.
4057 */
4058void
4059ring_buffer_read_prepare_sync(void)
4060{
4061        synchronize_sched();
4062}
4063EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
4064
4065/**
4066 * ring_buffer_read_start - start a non consuming read of the buffer
4067 * @iter: The iterator returned by ring_buffer_read_prepare
4068 *
4069 * This finalizes the startup of an iteration through the buffer.
4070 * The iterator comes from a call to ring_buffer_read_prepare and
4071 * an intervening ring_buffer_read_prepare_sync must have been
4072 * performed.
4073 *
4074 * Must be paired with ring_buffer_read_finish.
4075 */
4076void
4077ring_buffer_read_start(struct ring_buffer_iter *iter)
4078{
4079        struct ring_buffer_per_cpu *cpu_buffer;
4080        unsigned long flags;
4081
4082        if (!iter)
4083                return;
4084
4085        cpu_buffer = iter->cpu_buffer;
4086
4087        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4088        arch_spin_lock(&cpu_buffer->lock);
4089        rb_iter_reset(iter);
4090        arch_spin_unlock(&cpu_buffer->lock);
4091        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4092}
4093EXPORT_SYMBOL_GPL(ring_buffer_read_start);
4094
4095/**
4096 * ring_buffer_read_finish - finish reading the iterator of the buffer
4097 * @iter: The iterator retrieved by ring_buffer_start
4098 *
4099 * This re-enables the recording to the buffer, and frees the
4100 * iterator.
4101 */
4102void
4103ring_buffer_read_finish(struct ring_buffer_iter *iter)
4104{
4105        struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4106        unsigned long flags;
4107
4108        /*
4109         * Ring buffer is disabled from recording, here's a good place
4110         * to check the integrity of the ring buffer.
4111         * Must prevent readers from trying to read, as the check
4112         * clears the HEAD page and readers require it.
4113         */
4114        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4115        rb_check_pages(cpu_buffer);
4116        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4117
4118        atomic_dec(&cpu_buffer->record_disabled);
4119        atomic_dec(&cpu_buffer->buffer->resize_disabled);
4120        kfree(iter);
4121}
4122EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
4123
4124/**
4125 * ring_buffer_read - read the next item in the ring buffer by the iterator
4126 * @iter: The ring buffer iterator
4127 * @ts: The time stamp of the event read.
4128 *
4129 * This reads the next event in the ring buffer and increments the iterator.
4130 */
4131struct ring_buffer_event *
4132ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
4133{
4134        struct ring_buffer_event *event;
4135        struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4136        unsigned long flags;
4137
4138        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4139 again:
4140        event = rb_iter_peek(iter, ts);
4141        if (!event)
4142                goto out;
4143
4144        if (event->type_len == RINGBUF_TYPE_PADDING)
4145                goto again;
4146
4147        rb_advance_iter(iter);
4148 out:
4149        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4150
4151        return event;
4152}
4153EXPORT_SYMBOL_GPL(ring_buffer_read);
4154
4155/**
4156 * ring_buffer_size - return the size of the ring buffer (in bytes)
4157 * @buffer: The ring buffer.
4158 */
4159unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
4160{
4161        /*
4162         * Earlier, this method returned
4163         *      BUF_PAGE_SIZE * buffer->nr_pages
4164         * Since the nr_pages field is now removed, we have converted this to
4165         * return the per cpu buffer value.
4166         */
4167        if (!cpumask_test_cpu(cpu, buffer->cpumask))
4168                return 0;
4169
4170        return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
4171}
4172EXPORT_SYMBOL_GPL(ring_buffer_size);
4173
4174static void
4175rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
4176{
4177        rb_head_page_deactivate(cpu_buffer);
4178
4179        cpu_buffer->head_page
4180                = list_entry(cpu_buffer->pages, struct buffer_page, list);
4181        local_set(&cpu_buffer->head_page->write, 0);
4182        local_set(&cpu_buffer->head_page->entries, 0);
4183        local_set(&cpu_buffer->head_page->page->commit, 0);
4184
4185        cpu_buffer->head_page->read = 0;
4186
4187        cpu_buffer->tail_page = cpu_buffer->head_page;
4188        cpu_buffer->commit_page = cpu_buffer->head_page;
4189
4190        INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
4191        INIT_LIST_HEAD(&cpu_buffer->new_pages);
4192        local_set(&cpu_buffer->reader_page->write, 0);
4193        local_set(&cpu_buffer->reader_page->entries, 0);
4194        local_set(&cpu_buffer->reader_page->page->commit, 0);
4195        cpu_buffer->reader_page->read = 0;
4196
4197        local_set(&cpu_buffer->entries_bytes, 0);
4198        local_set(&cpu_buffer->overrun, 0);
4199        local_set(&cpu_buffer->commit_overrun, 0);
4200        local_set(&cpu_buffer->dropped_events, 0);
4201        local_set(&cpu_buffer->entries, 0);
4202        local_set(&cpu_buffer->committing, 0);
4203        local_set(&cpu_buffer->commits, 0);
4204        cpu_buffer->read = 0;
4205        cpu_buffer->read_bytes = 0;
4206
4207        cpu_buffer->write_stamp = 0;
4208        cpu_buffer->read_stamp = 0;
4209
4210        cpu_buffer->lost_events = 0;
4211        cpu_buffer->last_overrun = 0;
4212
4213        rb_head_page_activate(cpu_buffer);
4214}
4215
4216/**
4217 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
4218 * @buffer: The ring buffer to reset a per cpu buffer of
4219 * @cpu: The CPU buffer to be reset
4220 */
4221void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
4222{
4223        struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4224        unsigned long flags;
4225
4226        if (!cpumask_test_cpu(cpu, buffer->cpumask))
4227                return;
4228
4229        atomic_inc(&buffer->resize_disabled);
4230        atomic_inc(&cpu_buffer->record_disabled);
4231
4232        /* Make sure all commits have finished */
4233        synchronize_sched();
4234
4235        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4236
4237        if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
4238                goto out;
4239
4240        arch_spin_lock(&cpu_buffer->lock);
4241
4242        rb_reset_cpu(cpu_buffer);
4243
4244        arch_spin_unlock(&cpu_buffer->lock);
4245
4246 out:
4247        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4248
4249        atomic_dec(&cpu_buffer->record_disabled);
4250        atomic_dec(&buffer->resize_disabled);
4251}
4252EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
4253
4254/**
4255 * ring_buffer_reset - reset a ring buffer
4256 * @buffer: The ring buffer to reset all cpu buffers
4257 */
4258void ring_buffer_reset(struct ring_buffer *buffer)
4259{
4260        int cpu;
4261
4262        for_each_buffer_cpu(buffer, cpu)
4263                ring_buffer_reset_cpu(buffer, cpu);
4264}
4265EXPORT_SYMBOL_GPL(ring_buffer_reset);
4266
4267/**
4268 * rind_buffer_empty - is the ring buffer empty?
4269 * @buffer: The ring buffer to test
4270 */
4271bool ring_buffer_empty(struct ring_buffer *buffer)
4272{
4273        struct ring_buffer_per_cpu *cpu_buffer;
4274        unsigned long flags;
4275        bool dolock;
4276        int cpu;
4277        int ret;
4278
4279        /* yes this is racy, but if you don't like the race, lock the buffer */
4280        for_each_buffer_cpu(buffer, cpu) {
4281                cpu_buffer = buffer->buffers[cpu];
4282                local_irq_save(flags);
4283                dolock = rb_reader_lock(cpu_buffer);
4284                ret = rb_per_cpu_empty(cpu_buffer);
4285                rb_reader_unlock(cpu_buffer, dolock);
4286                local_irq_restore(flags);
4287
4288                if (!ret)
4289                        return false;
4290        }
4291
4292        return true;
4293}
4294EXPORT_SYMBOL_GPL(ring_buffer_empty);
4295
4296/**
4297 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
4298 * @buffer: The ring buffer
4299 * @cpu: The CPU buffer to test
4300 */
4301bool ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
4302{
4303        struct ring_buffer_per_cpu *cpu_buffer;
4304        unsigned long flags;
4305        bool dolock;
4306        int ret;
4307
4308        if (!cpumask_test_cpu(cpu, buffer->cpumask))
4309                return true;
4310
4311        cpu_buffer = buffer->buffers[cpu];
4312        local_irq_save(flags);
4313        dolock = rb_reader_lock(cpu_buffer);
4314        ret = rb_per_cpu_empty(cpu_buffer);
4315        rb_reader_unlock(cpu_buffer, dolock);
4316        local_irq_restore(flags);
4317
4318        return ret;
4319}
4320EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
4321
4322#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
4323/**
4324 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
4325 * @buffer_a: One buffer to swap with
4326 * @buffer_b: The other buffer to swap with
4327 *
4328 * This function is useful for tracers that want to take a "snapshot"
4329 * of a CPU buffer and has another back up buffer lying around.
4330 * it is expected that the tracer handles the cpu buffer not being
4331 * used at the moment.
4332 */
4333int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
4334                         struct ring_buffer *buffer_b, int cpu)
4335{
4336        struct ring_buffer_per_cpu *cpu_buffer_a;
4337        struct ring_buffer_per_cpu *cpu_buffer_b;
4338        int ret = -EINVAL;
4339
4340        if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
4341            !cpumask_test_cpu(cpu, buffer_b->cpumask))
4342                goto out;
4343
4344        cpu_buffer_a = buffer_a->buffers[cpu];
4345        cpu_buffer_b = buffer_b->buffers[cpu];
4346
4347        /* At least make sure the two buffers are somewhat the same */
4348        if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
4349                goto out;
4350
4351        ret = -EAGAIN;
4352
4353        if (atomic_read(&buffer_a->record_disabled))
4354                goto out;
4355
4356        if (atomic_read(&buffer_b->record_disabled))
4357                goto out;
4358
4359        if (atomic_read(&cpu_buffer_a->record_disabled))
4360                goto out;
4361
4362        if (atomic_read(&cpu_buffer_b->record_disabled))
4363                goto out;
4364
4365        /*
4366         * We can't do a synchronize_sched here because this
4367         * function can be called in atomic context.
4368         * Normally this will be called from the same CPU as cpu.
4369         * If not it's up to the caller to protect this.
4370         */
4371        atomic_inc(&cpu_buffer_a->record_disabled);
4372        atomic_inc(&cpu_buffer_b->record_disabled);
4373
4374        ret = -EBUSY;
4375        if (local_read(&cpu_buffer_a->committing))
4376                goto out_dec;
4377        if (local_read(&cpu_buffer_b->committing))
4378                goto out_dec;
4379
4380        buffer_a->buffers[cpu] = cpu_buffer_b;
4381        buffer_b->buffers[cpu] = cpu_buffer_a;
4382
4383        cpu_buffer_b->buffer = buffer_a;
4384        cpu_buffer_a->buffer = buffer_b;
4385
4386        ret = 0;
4387
4388out_dec:
4389        atomic_dec(&cpu_buffer_a->record_disabled);
4390        atomic_dec(&cpu_buffer_b->record_disabled);
4391out:
4392        return ret;
4393}
4394EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
4395#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
4396
4397/**
4398 * ring_buffer_alloc_read_page - allocate a page to read from buffer
4399 * @buffer: the buffer to allocate for.
4400 * @cpu: the cpu buffer to allocate.
4401 *
4402 * This function is used in conjunction with ring_buffer_read_page.
4403 * When reading a full page from the ring buffer, these functions
4404 * can be used to speed up the process. The calling function should
4405 * allocate a few pages first with this function. Then when it
4406 * needs to get pages from the ring buffer, it passes the result
4407 * of this function into ring_buffer_read_page, which will swap
4408 * the page that was allocated, with the read page of the buffer.
4409 *
4410 * Returns:
4411 *  The page allocated, or NULL on error.
4412 */
4413void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
4414{
4415        struct buffer_data_page *bpage;
4416        struct page *page;
4417
4418        page = alloc_pages_node(cpu_to_node(cpu),
4419                                GFP_KERNEL | __GFP_NORETRY, 0);
4420        if (!page)
4421                return NULL;
4422
4423        bpage = page_address(page);
4424
4425        rb_init_page(bpage);
4426
4427        return bpage;
4428}
4429EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
4430
4431/**
4432 * ring_buffer_free_read_page - free an allocated read page
4433 * @buffer: the buffer the page was allocate for
4434 * @data: the page to free
4435 *
4436 * Free a page allocated from ring_buffer_alloc_read_page.
4437 */
4438void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
4439{
4440        free_page((unsigned long)data);
4441}
4442EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
4443
4444/**
4445 * ring_buffer_read_page - extract a page from the ring buffer
4446 * @buffer: buffer to extract from
4447 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
4448 * @len: amount to extract
4449 * @cpu: the cpu of the buffer to extract
4450 * @full: should the extraction only happen when the page is full.
4451 *
4452 * This function will pull out a page from the ring buffer and consume it.
4453 * @data_page must be the address of the variable that was returned
4454 * from ring_buffer_alloc_read_page. This is because the page might be used
4455 * to swap with a page in the ring buffer.
4456 *
4457 * for example:
4458 *      rpage = ring_buffer_alloc_read_page(buffer, cpu);
4459 *      if (!rpage)
4460 *              return error;
4461 *      ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
4462 *      if (ret >= 0)
4463 *              process_page(rpage, ret);
4464 *
4465 * When @full is set, the function will not return true unless
4466 * the writer is off the reader page.
4467 *
4468 * Note: it is up to the calling functions to handle sleeps and wakeups.
4469 *  The ring buffer can be used anywhere in the kernel and can not
4470 *  blindly call wake_up. The layer that uses the ring buffer must be
4471 *  responsible for that.
4472 *
4473 * Returns:
4474 *  >=0 if data has been transferred, returns the offset of consumed data.
4475 *  <0 if no data has been transferred.
4476 */
4477int ring_buffer_read_page(struct ring_buffer *buffer,
4478                          void **data_page, size_t len, int cpu, int full)
4479{
4480        struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4481        struct ring_buffer_event *event;
4482        struct buffer_data_page *bpage;
4483        struct buffer_page *reader;
4484        unsigned long missed_events;
4485        unsigned long flags;
4486        unsigned int commit;
4487        unsigned int read;
4488        u64 save_timestamp;
4489        int ret = -1;
4490
4491        if (!cpumask_test_cpu(cpu, buffer->cpumask))
4492                goto out;
4493
4494        /*
4495         * If len is not big enough to hold the page header, then
4496         * we can not copy anything.
4497         */
4498        if (len <= BUF_PAGE_HDR_SIZE)
4499                goto out;
4500
4501        len -= BUF_PAGE_HDR_SIZE;
4502
4503        if (!data_page)
4504                goto out;
4505
4506        bpage = *data_page;
4507        if (!bpage)
4508                goto out;
4509
4510        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4511
4512        reader = rb_get_reader_page(cpu_buffer);
4513        if (!reader)
4514                goto out_unlock;
4515
4516        event = rb_reader_event(cpu_buffer);
4517
4518        read = reader->read;
4519        commit = rb_page_commit(reader);
4520
4521        /* Check if any events were dropped */
4522        missed_events = cpu_buffer->lost_events;
4523
4524        /*
4525         * If this page has been partially read or
4526         * if len is not big enough to read the rest of the page or
4527         * a writer is still on the page, then
4528         * we must copy the data from the page to the buffer.
4529         * Otherwise, we can simply swap the page with the one passed in.
4530         */
4531        if (read || (len < (commit - read)) ||
4532            cpu_buffer->reader_page == cpu_buffer->commit_page) {
4533                struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
4534                unsigned int rpos = read;
4535                unsigned int pos = 0;
4536                unsigned int size;
4537
4538                if (full)
4539                        goto out_unlock;
4540
4541                if (len > (commit - read))
4542                        len = (commit - read);
4543
4544                /* Always keep the time extend and data together */
4545                size = rb_event_ts_length(event);
4546
4547                if (len < size)
4548                        goto out_unlock;
4549
4550                /* save the current timestamp, since the user will need it */
4551                save_timestamp = cpu_buffer->read_stamp;
4552
4553                /* Need to copy one event at a time */
4554                do {
4555                        /* We need the size of one event, because
4556                         * rb_advance_reader only advances by one event,
4557                         * whereas rb_event_ts_length may include the size of
4558                         * one or two events.
4559                         * We have already ensured there's enough space if this
4560                         * is a time extend. */
4561                        size = rb_event_length(event);
4562                        memcpy(bpage->data + pos, rpage->data + rpos, size);
4563
4564                        len -= size;
4565
4566                        rb_advance_reader(cpu_buffer);
4567                        rpos = reader->read;
4568                        pos += size;
4569
4570                        if (rpos >= commit)
4571                                break;
4572
4573                        event = rb_reader_event(cpu_buffer);
4574                        /* Always keep the time extend and data together */
4575                        size = rb_event_ts_length(event);
4576                } while (len >= size);
4577
4578                /* update bpage */
4579                local_set(&bpage->commit, pos);
4580                bpage->time_stamp = save_timestamp;
4581
4582                /* we copied everything to the beginning */
4583                read = 0;
4584        } else {
4585                /* update the entry counter */
4586                cpu_buffer->read += rb_page_entries(reader);
4587                cpu_buffer->read_bytes += BUF_PAGE_SIZE;
4588
4589                /* swap the pages */
4590                rb_init_page(bpage);
4591                bpage = reader->page;
4592                reader->page = *data_page;
4593                local_set(&reader->write, 0);
4594                local_set(&reader->entries, 0);
4595                reader->read = 0;
4596                *data_page = bpage;
4597
4598                /*
4599                 * Use the real_end for the data size,
4600                 * This gives us a chance to store the lost events
4601                 * on the page.
4602                 */
4603                if (reader->real_end)
4604                        local_set(&bpage->commit, reader->real_end);
4605        }
4606        ret = read;
4607
4608        cpu_buffer->lost_events = 0;
4609
4610        commit = local_read(&bpage->commit);
4611        /*
4612         * Set a flag in the commit field if we lost events
4613         */
4614        if (missed_events) {
4615                /* If there is room at the end of the page to save the
4616                 * missed events, then record it there.
4617                 */
4618                if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
4619                        memcpy(&bpage->data[commit], &missed_events,
4620                               sizeof(missed_events));
4621                        local_add(RB_MISSED_STORED, &bpage->commit);
4622                        commit += sizeof(missed_events);
4623                }
4624                local_add(RB_MISSED_EVENTS, &bpage->commit);
4625        }
4626
4627        /*
4628         * This page may be off to user land. Zero it out here.
4629         */
4630        if (commit < BUF_PAGE_SIZE)
4631                memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
4632
4633 out_unlock:
4634        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4635
4636 out:
4637        return ret;
4638}
4639EXPORT_SYMBOL_GPL(ring_buffer_read_page);
4640
4641#ifdef CONFIG_HOTPLUG_CPU
4642static int rb_cpu_notify(struct notifier_block *self,
4643                         unsigned long action, void *hcpu)
4644{
4645        struct ring_buffer *buffer =
4646                container_of(self, struct ring_buffer, cpu_notify);
4647        long cpu = (long)hcpu;
4648        long nr_pages_same;
4649        int cpu_i;
4650        unsigned long nr_pages;
4651
4652        switch (action) {
4653        case CPU_UP_PREPARE:
4654        case CPU_UP_PREPARE_FROZEN:
4655                if (cpumask_test_cpu(cpu, buffer->cpumask))
4656                        return NOTIFY_OK;
4657
4658                nr_pages = 0;
4659                nr_pages_same = 1;
4660                /* check if all cpu sizes are same */
4661                for_each_buffer_cpu(buffer, cpu_i) {
4662                        /* fill in the size from first enabled cpu */
4663                        if (nr_pages == 0)
4664                                nr_pages = buffer->buffers[cpu_i]->nr_pages;
4665                        if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
4666                                nr_pages_same = 0;
4667                                break;
4668                        }
4669                }
4670                /* allocate minimum pages, user can later expand it */
4671                if (!nr_pages_same)
4672                        nr_pages = 2;
4673                buffer->buffers[cpu] =
4674                        rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
4675                if (!buffer->buffers[cpu]) {
4676                        WARN(1, "failed to allocate ring buffer on CPU %ld\n",
4677                             cpu);
4678                        return NOTIFY_OK;
4679                }
4680                smp_wmb();
4681                cpumask_set_cpu(cpu, buffer->cpumask);
4682                break;
4683        case CPU_DOWN_PREPARE:
4684        case CPU_DOWN_PREPARE_FROZEN:
4685                /*
4686                 * Do nothing.
4687                 *  If we were to free the buffer, then the user would
4688                 *  lose any trace that was in the buffer.
4689                 */
4690                break;
4691        default:
4692                break;
4693        }
4694        return NOTIFY_OK;
4695}
4696#endif
4697
4698#ifdef CONFIG_RING_BUFFER_STARTUP_TEST
4699/*
4700 * This is a basic integrity check of the ring buffer.
4701 * Late in the boot cycle this test will run when configured in.
4702 * It will kick off a thread per CPU that will go into a loop
4703 * writing to the per cpu ring buffer various sizes of data.
4704 * Some of the data will be large items, some small.
4705 *
4706 * Another thread is created that goes into a spin, sending out
4707 * IPIs to the other CPUs to also write into the ring buffer.
4708 * this is to test the nesting ability of the buffer.
4709 *
4710 * Basic stats are recorded and reported. If something in the
4711 * ring buffer should happen that's not expected, a big warning
4712 * is displayed and all ring buffers are disabled.
4713 */
4714static struct task_struct *rb_threads[NR_CPUS] __initdata;
4715
4716struct rb_test_data {
4717        struct ring_buffer      *buffer;
4718        unsigned long           events;
4719        unsigned long           bytes_written;
4720        unsigned long           bytes_alloc;
4721        unsigned long           bytes_dropped;
4722        unsigned long           events_nested;
4723        unsigned long           bytes_written_nested;
4724        unsigned long           bytes_alloc_nested;
4725        unsigned long           bytes_dropped_nested;
4726        int                     min_size_nested;
4727        int                     max_size_nested;
4728        int                     max_size;
4729        int                     min_size;
4730        int                     cpu;
4731        int                     cnt;
4732};
4733
4734static struct rb_test_data rb_data[NR_CPUS] __initdata;
4735
4736/* 1 meg per cpu */
4737#define RB_TEST_BUFFER_SIZE     1048576
4738
4739static char rb_string[] __initdata =
4740        "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
4741        "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
4742        "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
4743
4744static bool rb_test_started __initdata;
4745
4746struct rb_item {
4747        int size;
4748        char str[];
4749};
4750
4751static __init int rb_write_something(struct rb_test_data *data, bool nested)
4752{
4753        struct ring_buffer_event *event;
4754        struct rb_item *item;
4755        bool started;
4756        int event_len;
4757        int size;
4758        int len;
4759        int cnt;
4760
4761        /* Have nested writes different that what is written */
4762        cnt = data->cnt + (nested ? 27 : 0);
4763
4764        /* Multiply cnt by ~e, to make some unique increment */
4765        size = (data->cnt * 68 / 25) % (sizeof(rb_string) - 1);
4766
4767        len = size + sizeof(struct rb_item);
4768
4769        started = rb_test_started;
4770        /* read rb_test_started before checking buffer enabled */
4771        smp_rmb();
4772
4773        event = ring_buffer_lock_reserve(data->buffer, len);
4774        if (!event) {
4775                /* Ignore dropped events before test starts. */
4776                if (started) {
4777                        if (nested)
4778                                data->bytes_dropped += len;
4779                        else
4780                                data->bytes_dropped_nested += len;
4781                }
4782                return len;
4783        }
4784
4785        event_len = ring_buffer_event_length(event);
4786
4787        if (RB_WARN_ON(data->buffer, event_len < len))
4788                goto out;
4789
4790        item = ring_buffer_event_data(event);
4791        item->size = size;
4792        memcpy(item->str, rb_string, size);
4793
4794        if (nested) {
4795                data->bytes_alloc_nested += event_len;
4796                data->bytes_written_nested += len;
4797                data->events_nested++;
4798                if (!data->min_size_nested || len < data->min_size_nested)
4799                        data->min_size_nested = len;
4800                if (len > data->max_size_nested)
4801                        data->max_size_nested = len;
4802        } else {
4803                data->bytes_alloc += event_len;
4804                data->bytes_written += len;
4805                data->events++;
4806                if (!data->min_size || len < data->min_size)
4807                        data->max_size = len;
4808                if (len > data->max_size)
4809                        data->max_size = len;
4810        }
4811
4812 out:
4813        ring_buffer_unlock_commit(data->buffer, event);
4814
4815        return 0;
4816}
4817
4818static __init int rb_test(void *arg)
4819{
4820        struct rb_test_data *data = arg;
4821
4822        while (!kthread_should_stop()) {
4823                rb_write_something(data, false);
4824                data->cnt++;
4825
4826                set_current_state(TASK_INTERRUPTIBLE);
4827                /* Now sleep between a min of 100-300us and a max of 1ms */
4828                usleep_range(((data->cnt % 3) + 1) * 100, 1000);
4829        }
4830
4831        return 0;
4832}
4833
4834static __init void rb_ipi(void *ignore)
4835{
4836        struct rb_test_data *data;
4837        int cpu = smp_processor_id();
4838
4839        data = &rb_data[cpu];
4840        rb_write_something(data, true);
4841}
4842
4843static __init int rb_hammer_test(void *arg)
4844{
4845        while (!kthread_should_stop()) {
4846
4847                /* Send an IPI to all cpus to write data! */
4848                smp_call_function(rb_ipi, NULL, 1);
4849                /* No sleep, but for non preempt, let others run */
4850                schedule();
4851        }
4852
4853        return 0;
4854}
4855
4856static __init int test_ringbuffer(void)
4857{
4858        struct task_struct *rb_hammer;
4859        struct ring_buffer *buffer;
4860        int cpu;
4861        int ret = 0;
4862
4863        pr_info("Running ring buffer tests...\n");
4864
4865        buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
4866        if (WARN_ON(!buffer))
4867                return 0;
4868
4869        /* Disable buffer so that threads can't write to it yet */
4870        ring_buffer_record_off(buffer);
4871
4872        for_each_online_cpu(cpu) {
4873                rb_data[cpu].buffer = buffer;
4874                rb_data[cpu].cpu = cpu;
4875                rb_data[cpu].cnt = cpu;
4876                rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu],
4877                                                 "rbtester/%d", cpu);
4878                if (WARN_ON(IS_ERR(rb_threads[cpu]))) {
4879                        pr_cont("FAILED\n");
4880                        ret = PTR_ERR(rb_threads[cpu]);
4881                        goto out_free;
4882                }
4883
4884                kthread_bind(rb_threads[cpu], cpu);
4885                wake_up_process(rb_threads[cpu]);
4886        }
4887
4888        /* Now create the rb hammer! */
4889        rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
4890        if (WARN_ON(IS_ERR(rb_hammer))) {
4891                pr_cont("FAILED\n");
4892                ret = PTR_ERR(rb_hammer);
4893                goto out_free;
4894        }
4895
4896        ring_buffer_record_on(buffer);
4897        /*
4898         * Show buffer is enabled before setting rb_test_started.
4899         * Yes there's a small race window where events could be
4900         * dropped and the thread wont catch it. But when a ring
4901         * buffer gets enabled, there will always be some kind of
4902         * delay before other CPUs see it. Thus, we don't care about
4903         * those dropped events. We care about events dropped after
4904         * the threads see that the buffer is active.
4905         */
4906        smp_wmb();
4907        rb_test_started = true;
4908
4909        set_current_state(TASK_INTERRUPTIBLE);
4910        /* Just run for 10 seconds */;
4911        schedule_timeout(10 * HZ);
4912
4913        kthread_stop(rb_hammer);
4914
4915 out_free:
4916        for_each_online_cpu(cpu) {
4917                if (!rb_threads[cpu])
4918                        break;
4919                kthread_stop(rb_threads[cpu]);
4920        }
4921        if (ret) {
4922                ring_buffer_free(buffer);
4923                return ret;
4924        }
4925
4926        /* Report! */
4927        pr_info("finished\n");
4928        for_each_online_cpu(cpu) {
4929                struct ring_buffer_event *event;
4930                struct rb_test_data *data = &rb_data[cpu];
4931                struct rb_item *item;
4932                unsigned long total_events;
4933                unsigned long total_dropped;
4934                unsigned long total_written;
4935                unsigned long total_alloc;
4936                unsigned long total_read = 0;
4937                unsigned long total_size = 0;
4938                unsigned long total_len = 0;
4939                unsigned long total_lost = 0;
4940                unsigned long lost;
4941                int big_event_size;
4942                int small_event_size;
4943
4944                ret = -1;
4945
4946                total_events = data->events + data->events_nested;
4947                total_written = data->bytes_written + data->bytes_written_nested;
4948                total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
4949                total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
4950
4951                big_event_size = data->max_size + data->max_size_nested;
4952                small_event_size = data->min_size + data->min_size_nested;
4953
4954                pr_info("CPU %d:\n", cpu);
4955                pr_info("              events:    %ld\n", total_events);
4956                pr_info("       dropped bytes:    %ld\n", total_dropped);
4957                pr_info("       alloced bytes:    %ld\n", total_alloc);
4958                pr_info("       written bytes:    %ld\n", total_written);
4959                pr_info("       biggest event:    %d\n", big_event_size);
4960                pr_info("      smallest event:    %d\n", small_event_size);
4961
4962                if (RB_WARN_ON(buffer, total_dropped))
4963                        break;
4964
4965                ret = 0;
4966
4967                while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
4968                        total_lost += lost;
4969                        item = ring_buffer_event_data(event);
4970                        total_len += ring_buffer_event_length(event);
4971                        total_size += item->size + sizeof(struct rb_item);
4972                        if (memcmp(&item->str[0], rb_string, item->size) != 0) {
4973                                pr_info("FAILED!\n");
4974                                pr_info("buffer had: %.*s\n", item->size, item->str);
4975                                pr_info("expected:   %.*s\n", item->size, rb_string);
4976                                RB_WARN_ON(buffer, 1);
4977                                ret = -1;
4978                                break;
4979                        }
4980                        total_read++;
4981                }
4982                if (ret)
4983                        break;
4984
4985                ret = -1;
4986
4987                pr_info("         read events:   %ld\n", total_read);
4988                pr_info("         lost events:   %ld\n", total_lost);
4989                pr_info("        total events:   %ld\n", total_lost + total_read);
4990                pr_info("  recorded len bytes:   %ld\n", total_len);
4991                pr_info(" recorded size bytes:   %ld\n", total_size);
4992                if (total_lost)
4993                        pr_info(" With dropped events, record len and size may not match\n"
4994                                " alloced and written from above\n");
4995                if (!total_lost) {
4996                        if (RB_WARN_ON(buffer, total_len != total_alloc ||
4997                                       total_size != total_written))
4998                                break;
4999                }
5000                if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
5001                        break;
5002
5003                ret = 0;
5004        }
5005        if (!ret)
5006                pr_info("Ring buffer PASSED!\n");
5007
5008        ring_buffer_free(buffer);
5009        return 0;
5010}
5011
5012late_initcall(test_ringbuffer);
5013#endif /* CONFIG_RING_BUFFER_STARTUP_TEST */
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