arm64: alternatives: add enable parameter to conditional asm macros
[linux/fpc-iii.git] / kernel / trace / ring_buffer.c
blob6260717c18e3c6fb8eefa4cfcc185ab8322a6929
1 /*
2 * Generic ring buffer
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>
26 #include <asm/local.h>
28 static void update_pages_handler(struct work_struct *work);
31 * The ring buffer header is special. We must manually up keep it.
33 int ring_buffer_print_entry_header(struct trace_seq *s)
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);
47 return !trace_seq_has_overflowed(s);
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.
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.
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).
64 * Here's some silly ASCII art.
66 * +------+
67 * |reader| RING BUFFER
68 * |page |
69 * +------+ +---+ +---+ +---+
70 * | |-->| |-->| |
71 * +---+ +---+ +---+
72 * ^ |
73 * | |
74 * +---------------+
77 * +------+
78 * |reader| RING BUFFER
79 * |page |------------------v
80 * +------+ +---+ +---+ +---+
81 * | |-->| |-->| |
82 * +---+ +---+ +---+
83 * ^ |
84 * | |
85 * +---------------+
88 * +------+
89 * |reader| RING BUFFER
90 * |page |------------------v
91 * +------+ +---+ +---+ +---+
92 * ^ | |-->| |-->| |
93 * | +---+ +---+ +---+
94 * | |
95 * | |
96 * +------------------------------+
99 * +------+
100 * |buffer| RING BUFFER
101 * |page |------------------v
102 * +------+ +---+ +---+ +---+
103 * ^ | | | |-->| |
104 * | New +---+ +---+ +---+
105 * | Reader------^ |
106 * | page |
107 * +------------------------------+
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.
114 * We will be using cmpxchg soon to make all this lockless.
118 /* Used for individual buffers (after the counter) */
119 #define RB_BUFFER_OFF (1 << 20)
121 #define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
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 */
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
136 #define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
138 /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
139 #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
141 enum {
142 RB_LEN_TIME_EXTEND = 8,
143 RB_LEN_TIME_STAMP = 16,
146 #define skip_time_extend(event) \
147 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
149 static inline int rb_null_event(struct ring_buffer_event *event)
151 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
154 static void rb_event_set_padding(struct ring_buffer_event *event)
156 /* padding has a NULL time_delta */
157 event->type_len = RINGBUF_TYPE_PADDING;
158 event->time_delta = 0;
161 static unsigned
162 rb_event_data_length(struct ring_buffer_event *event)
164 unsigned length;
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;
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.
178 static inline unsigned
179 rb_event_length(struct ring_buffer_event *event)
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;
188 case RINGBUF_TYPE_TIME_EXTEND:
189 return RB_LEN_TIME_EXTEND;
191 case RINGBUF_TYPE_TIME_STAMP:
192 return RB_LEN_TIME_STAMP;
194 case RINGBUF_TYPE_DATA:
195 return rb_event_data_length(event);
196 default:
197 BUG();
199 /* not hit */
200 return 0;
204 * Return total length of time extend and data,
205 * or just the event length for all other events.
207 static inline unsigned
208 rb_event_ts_length(struct ring_buffer_event *event)
210 unsigned len = 0;
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);
217 return len + rb_event_length(event);
221 * ring_buffer_event_length - return the length of the event
222 * @event: the event to get the length of
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.
230 unsigned ring_buffer_event_length(struct ring_buffer_event *event)
232 unsigned length;
234 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
235 event = skip_time_extend(event);
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;
245 EXPORT_SYMBOL_GPL(ring_buffer_event_length);
247 /* inline for ring buffer fast paths */
248 static void *
249 rb_event_data(struct ring_buffer_event *event)
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];
262 * ring_buffer_event_data - return the data of the event
263 * @event: the event to get the data from
265 void *ring_buffer_event_data(struct ring_buffer_event *event)
267 return rb_event_data(event);
269 EXPORT_SYMBOL_GPL(ring_buffer_event_data);
271 #define for_each_buffer_cpu(buffer, cpu) \
272 for_each_cpu(cpu, buffer->cpumask)
274 #define TS_SHIFT 27
275 #define TS_MASK ((1ULL << TS_SHIFT) - 1)
276 #define TS_DELTA_TEST (~TS_MASK)
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)
283 struct 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 */
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.
297 struct 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 */
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.
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.
316 * The counter is 20 bits, and the state data is 12.
318 #define RB_WRITE_MASK 0xfffff
319 #define RB_WRITE_INTCNT (1 << 20)
321 static void rb_init_page(struct buffer_data_page *bpage)
323 local_set(&bpage->commit, 0);
327 * ring_buffer_page_len - the size of data on the page.
328 * @page: The page to read
330 * Returns the amount of data on the page, including buffer page header.
332 size_t ring_buffer_page_len(void *page)
334 return local_read(&((struct buffer_data_page *)page)->commit)
335 + BUF_PAGE_HDR_SIZE;
339 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
340 * this issue out.
342 static void free_buffer_page(struct buffer_page *bpage)
344 free_page((unsigned long)bpage->page);
345 kfree(bpage);
349 * We need to fit the time_stamp delta into 27 bits.
351 static inline int test_time_stamp(u64 delta)
353 if (delta & TS_DELTA_TEST)
354 return 1;
355 return 0;
358 #define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
360 /* Max payload is BUF_PAGE_SIZE - header (8bytes) */
361 #define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
363 int ring_buffer_print_page_header(struct trace_seq *s)
365 struct buffer_data_page field;
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));
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));
378 trace_seq_printf(s, "\tfield: int overwrite;\t"
379 "offset:%u;\tsize:%u;\tsigned:%u;\n",
380 (unsigned int)offsetof(typeof(field), commit),
382 (unsigned int)is_signed_type(long));
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));
390 return !trace_seq_has_overflowed(s);
393 struct 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;
403 * Used for which event context the event is in.
404 * NMI = 0
405 * IRQ = 1
406 * SOFTIRQ = 2
407 * NORMAL = 3
409 * See trace_recursive_lock() comment below for more details.
411 enum {
412 RB_CTX_NMI,
413 RB_CTX_IRQ,
414 RB_CTX_SOFTIRQ,
415 RB_CTX_NORMAL,
416 RB_CTX_MAX
420 * head_page == tail_page && head == tail then buffer is empty.
422 struct ring_buffer_per_cpu {
423 int cpu;
424 atomic_t record_disabled;
425 struct ring_buffer *buffer;
426 raw_spinlock_t reader_lock; /* serialize readers */
427 arch_spinlock_t lock;
428 struct lock_class_key lock_key;
429 unsigned int nr_pages;
430 unsigned int current_context;
431 struct list_head *pages;
432 struct buffer_page *head_page; /* read from head */
433 struct buffer_page *tail_page; /* write to tail */
434 struct buffer_page *commit_page; /* committed pages */
435 struct buffer_page *reader_page;
436 unsigned long lost_events;
437 unsigned long last_overrun;
438 local_t entries_bytes;
439 local_t entries;
440 local_t overrun;
441 local_t commit_overrun;
442 local_t dropped_events;
443 local_t committing;
444 local_t commits;
445 unsigned long read;
446 unsigned long read_bytes;
447 u64 write_stamp;
448 u64 read_stamp;
449 /* ring buffer pages to update, > 0 to add, < 0 to remove */
450 int nr_pages_to_update;
451 struct list_head new_pages; /* new pages to add */
452 struct work_struct update_pages_work;
453 struct completion update_done;
455 struct rb_irq_work irq_work;
458 struct ring_buffer {
459 unsigned flags;
460 int cpus;
461 atomic_t record_disabled;
462 atomic_t resize_disabled;
463 cpumask_var_t cpumask;
465 struct lock_class_key *reader_lock_key;
467 struct mutex mutex;
469 struct ring_buffer_per_cpu **buffers;
471 #ifdef CONFIG_HOTPLUG_CPU
472 struct notifier_block cpu_notify;
473 #endif
474 u64 (*clock)(void);
476 struct rb_irq_work irq_work;
479 struct ring_buffer_iter {
480 struct ring_buffer_per_cpu *cpu_buffer;
481 unsigned long head;
482 struct buffer_page *head_page;
483 struct buffer_page *cache_reader_page;
484 unsigned long cache_read;
485 u64 read_stamp;
489 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
491 * Schedules a delayed work to wake up any task that is blocked on the
492 * ring buffer waiters queue.
494 static void rb_wake_up_waiters(struct irq_work *work)
496 struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
498 wake_up_all(&rbwork->waiters);
499 if (rbwork->wakeup_full) {
500 rbwork->wakeup_full = false;
501 wake_up_all(&rbwork->full_waiters);
506 * ring_buffer_wait - wait for input to the ring buffer
507 * @buffer: buffer to wait on
508 * @cpu: the cpu buffer to wait on
509 * @full: wait until a full page is available, if @cpu != RING_BUFFER_ALL_CPUS
511 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
512 * as data is added to any of the @buffer's cpu buffers. Otherwise
513 * it will wait for data to be added to a specific cpu buffer.
515 int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full)
517 struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer);
518 DEFINE_WAIT(wait);
519 struct rb_irq_work *work;
520 int ret = 0;
523 * Depending on what the caller is waiting for, either any
524 * data in any cpu buffer, or a specific buffer, put the
525 * caller on the appropriate wait queue.
527 if (cpu == RING_BUFFER_ALL_CPUS) {
528 work = &buffer->irq_work;
529 /* Full only makes sense on per cpu reads */
530 full = false;
531 } else {
532 if (!cpumask_test_cpu(cpu, buffer->cpumask))
533 return -ENODEV;
534 cpu_buffer = buffer->buffers[cpu];
535 work = &cpu_buffer->irq_work;
539 while (true) {
540 if (full)
541 prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
542 else
543 prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
546 * The events can happen in critical sections where
547 * checking a work queue can cause deadlocks.
548 * After adding a task to the queue, this flag is set
549 * only to notify events to try to wake up the queue
550 * using irq_work.
552 * We don't clear it even if the buffer is no longer
553 * empty. The flag only causes the next event to run
554 * irq_work to do the work queue wake up. The worse
555 * that can happen if we race with !trace_empty() is that
556 * an event will cause an irq_work to try to wake up
557 * an empty queue.
559 * There's no reason to protect this flag either, as
560 * the work queue and irq_work logic will do the necessary
561 * synchronization for the wake ups. The only thing
562 * that is necessary is that the wake up happens after
563 * a task has been queued. It's OK for spurious wake ups.
565 if (full)
566 work->full_waiters_pending = true;
567 else
568 work->waiters_pending = true;
570 if (signal_pending(current)) {
571 ret = -EINTR;
572 break;
575 if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
576 break;
578 if (cpu != RING_BUFFER_ALL_CPUS &&
579 !ring_buffer_empty_cpu(buffer, cpu)) {
580 unsigned long flags;
581 bool pagebusy;
583 if (!full)
584 break;
586 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
587 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
588 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
590 if (!pagebusy)
591 break;
594 schedule();
597 if (full)
598 finish_wait(&work->full_waiters, &wait);
599 else
600 finish_wait(&work->waiters, &wait);
602 return ret;
606 * ring_buffer_poll_wait - poll on buffer input
607 * @buffer: buffer to wait on
608 * @cpu: the cpu buffer to wait on
609 * @filp: the file descriptor
610 * @poll_table: The poll descriptor
612 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
613 * as data is added to any of the @buffer's cpu buffers. Otherwise
614 * it will wait for data to be added to a specific cpu buffer.
616 * Returns POLLIN | POLLRDNORM if data exists in the buffers,
617 * zero otherwise.
619 int ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
620 struct file *filp, poll_table *poll_table)
622 struct ring_buffer_per_cpu *cpu_buffer;
623 struct rb_irq_work *work;
625 if (cpu == RING_BUFFER_ALL_CPUS)
626 work = &buffer->irq_work;
627 else {
628 if (!cpumask_test_cpu(cpu, buffer->cpumask))
629 return -EINVAL;
631 cpu_buffer = buffer->buffers[cpu];
632 work = &cpu_buffer->irq_work;
635 poll_wait(filp, &work->waiters, poll_table);
636 work->waiters_pending = true;
638 * There's a tight race between setting the waiters_pending and
639 * checking if the ring buffer is empty. Once the waiters_pending bit
640 * is set, the next event will wake the task up, but we can get stuck
641 * if there's only a single event in.
643 * FIXME: Ideally, we need a memory barrier on the writer side as well,
644 * but adding a memory barrier to all events will cause too much of a
645 * performance hit in the fast path. We only need a memory barrier when
646 * the buffer goes from empty to having content. But as this race is
647 * extremely small, and it's not a problem if another event comes in, we
648 * will fix it later.
650 smp_mb();
652 if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
653 (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
654 return POLLIN | POLLRDNORM;
655 return 0;
658 /* buffer may be either ring_buffer or ring_buffer_per_cpu */
659 #define RB_WARN_ON(b, cond) \
660 ({ \
661 int _____ret = unlikely(cond); \
662 if (_____ret) { \
663 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
664 struct ring_buffer_per_cpu *__b = \
665 (void *)b; \
666 atomic_inc(&__b->buffer->record_disabled); \
667 } else \
668 atomic_inc(&b->record_disabled); \
669 WARN_ON(1); \
671 _____ret; \
674 /* Up this if you want to test the TIME_EXTENTS and normalization */
675 #define DEBUG_SHIFT 0
677 static inline u64 rb_time_stamp(struct ring_buffer *buffer)
679 /* shift to debug/test normalization and TIME_EXTENTS */
680 return buffer->clock() << DEBUG_SHIFT;
683 u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
685 u64 time;
687 preempt_disable_notrace();
688 time = rb_time_stamp(buffer);
689 preempt_enable_no_resched_notrace();
691 return time;
693 EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
695 void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
696 int cpu, u64 *ts)
698 /* Just stupid testing the normalize function and deltas */
699 *ts >>= DEBUG_SHIFT;
701 EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
704 * Making the ring buffer lockless makes things tricky.
705 * Although writes only happen on the CPU that they are on,
706 * and they only need to worry about interrupts. Reads can
707 * happen on any CPU.
709 * The reader page is always off the ring buffer, but when the
710 * reader finishes with a page, it needs to swap its page with
711 * a new one from the buffer. The reader needs to take from
712 * the head (writes go to the tail). But if a writer is in overwrite
713 * mode and wraps, it must push the head page forward.
715 * Here lies the problem.
717 * The reader must be careful to replace only the head page, and
718 * not another one. As described at the top of the file in the
719 * ASCII art, the reader sets its old page to point to the next
720 * page after head. It then sets the page after head to point to
721 * the old reader page. But if the writer moves the head page
722 * during this operation, the reader could end up with the tail.
724 * We use cmpxchg to help prevent this race. We also do something
725 * special with the page before head. We set the LSB to 1.
727 * When the writer must push the page forward, it will clear the
728 * bit that points to the head page, move the head, and then set
729 * the bit that points to the new head page.
731 * We also don't want an interrupt coming in and moving the head
732 * page on another writer. Thus we use the second LSB to catch
733 * that too. Thus:
735 * head->list->prev->next bit 1 bit 0
736 * ------- -------
737 * Normal page 0 0
738 * Points to head page 0 1
739 * New head page 1 0
741 * Note we can not trust the prev pointer of the head page, because:
743 * +----+ +-----+ +-----+
744 * | |------>| T |---X--->| N |
745 * | |<------| | | |
746 * +----+ +-----+ +-----+
747 * ^ ^ |
748 * | +-----+ | |
749 * +----------| R |----------+ |
750 * | |<-----------+
751 * +-----+
753 * Key: ---X--> HEAD flag set in pointer
754 * T Tail page
755 * R Reader page
756 * N Next page
758 * (see __rb_reserve_next() to see where this happens)
760 * What the above shows is that the reader just swapped out
761 * the reader page with a page in the buffer, but before it
762 * could make the new header point back to the new page added
763 * it was preempted by a writer. The writer moved forward onto
764 * the new page added by the reader and is about to move forward
765 * again.
767 * You can see, it is legitimate for the previous pointer of
768 * the head (or any page) not to point back to itself. But only
769 * temporarially.
772 #define RB_PAGE_NORMAL 0UL
773 #define RB_PAGE_HEAD 1UL
774 #define RB_PAGE_UPDATE 2UL
777 #define RB_FLAG_MASK 3UL
779 /* PAGE_MOVED is not part of the mask */
780 #define RB_PAGE_MOVED 4UL
783 * rb_list_head - remove any bit
785 static struct list_head *rb_list_head(struct list_head *list)
787 unsigned long val = (unsigned long)list;
789 return (struct list_head *)(val & ~RB_FLAG_MASK);
793 * rb_is_head_page - test if the given page is the head page
795 * Because the reader may move the head_page pointer, we can
796 * not trust what the head page is (it may be pointing to
797 * the reader page). But if the next page is a header page,
798 * its flags will be non zero.
800 static inline int
801 rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
802 struct buffer_page *page, struct list_head *list)
804 unsigned long val;
806 val = (unsigned long)list->next;
808 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
809 return RB_PAGE_MOVED;
811 return val & RB_FLAG_MASK;
815 * rb_is_reader_page
817 * The unique thing about the reader page, is that, if the
818 * writer is ever on it, the previous pointer never points
819 * back to the reader page.
821 static int rb_is_reader_page(struct buffer_page *page)
823 struct list_head *list = page->list.prev;
825 return rb_list_head(list->next) != &page->list;
829 * rb_set_list_to_head - set a list_head to be pointing to head.
831 static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
832 struct list_head *list)
834 unsigned long *ptr;
836 ptr = (unsigned long *)&list->next;
837 *ptr |= RB_PAGE_HEAD;
838 *ptr &= ~RB_PAGE_UPDATE;
842 * rb_head_page_activate - sets up head page
844 static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
846 struct buffer_page *head;
848 head = cpu_buffer->head_page;
849 if (!head)
850 return;
853 * Set the previous list pointer to have the HEAD flag.
855 rb_set_list_to_head(cpu_buffer, head->list.prev);
858 static void rb_list_head_clear(struct list_head *list)
860 unsigned long *ptr = (unsigned long *)&list->next;
862 *ptr &= ~RB_FLAG_MASK;
866 * rb_head_page_dactivate - clears head page ptr (for free list)
868 static void
869 rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
871 struct list_head *hd;
873 /* Go through the whole list and clear any pointers found. */
874 rb_list_head_clear(cpu_buffer->pages);
876 list_for_each(hd, cpu_buffer->pages)
877 rb_list_head_clear(hd);
880 static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
881 struct buffer_page *head,
882 struct buffer_page *prev,
883 int old_flag, int new_flag)
885 struct list_head *list;
886 unsigned long val = (unsigned long)&head->list;
887 unsigned long ret;
889 list = &prev->list;
891 val &= ~RB_FLAG_MASK;
893 ret = cmpxchg((unsigned long *)&list->next,
894 val | old_flag, val | new_flag);
896 /* check if the reader took the page */
897 if ((ret & ~RB_FLAG_MASK) != val)
898 return RB_PAGE_MOVED;
900 return ret & RB_FLAG_MASK;
903 static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
904 struct buffer_page *head,
905 struct buffer_page *prev,
906 int old_flag)
908 return rb_head_page_set(cpu_buffer, head, prev,
909 old_flag, RB_PAGE_UPDATE);
912 static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
913 struct buffer_page *head,
914 struct buffer_page *prev,
915 int old_flag)
917 return rb_head_page_set(cpu_buffer, head, prev,
918 old_flag, RB_PAGE_HEAD);
921 static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
922 struct buffer_page *head,
923 struct buffer_page *prev,
924 int old_flag)
926 return rb_head_page_set(cpu_buffer, head, prev,
927 old_flag, RB_PAGE_NORMAL);
930 static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
931 struct buffer_page **bpage)
933 struct list_head *p = rb_list_head((*bpage)->list.next);
935 *bpage = list_entry(p, struct buffer_page, list);
938 static struct buffer_page *
939 rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
941 struct buffer_page *head;
942 struct buffer_page *page;
943 struct list_head *list;
944 int i;
946 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
947 return NULL;
949 /* sanity check */
950 list = cpu_buffer->pages;
951 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
952 return NULL;
954 page = head = cpu_buffer->head_page;
956 * It is possible that the writer moves the header behind
957 * where we started, and we miss in one loop.
958 * A second loop should grab the header, but we'll do
959 * three loops just because I'm paranoid.
961 for (i = 0; i < 3; i++) {
962 do {
963 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
964 cpu_buffer->head_page = page;
965 return page;
967 rb_inc_page(cpu_buffer, &page);
968 } while (page != head);
971 RB_WARN_ON(cpu_buffer, 1);
973 return NULL;
976 static int rb_head_page_replace(struct buffer_page *old,
977 struct buffer_page *new)
979 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
980 unsigned long val;
981 unsigned long ret;
983 val = *ptr & ~RB_FLAG_MASK;
984 val |= RB_PAGE_HEAD;
986 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
988 return ret == val;
992 * rb_tail_page_update - move the tail page forward
994 * Returns 1 if moved tail page, 0 if someone else did.
996 static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
997 struct buffer_page *tail_page,
998 struct buffer_page *next_page)
1000 struct buffer_page *old_tail;
1001 unsigned long old_entries;
1002 unsigned long old_write;
1003 int ret = 0;
1006 * The tail page now needs to be moved forward.
1008 * We need to reset the tail page, but without messing
1009 * with possible erasing of data brought in by interrupts
1010 * that have moved the tail page and are currently on it.
1012 * We add a counter to the write field to denote this.
1014 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1015 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1018 * Just make sure we have seen our old_write and synchronize
1019 * with any interrupts that come in.
1021 barrier();
1024 * If the tail page is still the same as what we think
1025 * it is, then it is up to us to update the tail
1026 * pointer.
1028 if (tail_page == cpu_buffer->tail_page) {
1029 /* Zero the write counter */
1030 unsigned long val = old_write & ~RB_WRITE_MASK;
1031 unsigned long eval = old_entries & ~RB_WRITE_MASK;
1034 * This will only succeed if an interrupt did
1035 * not come in and change it. In which case, we
1036 * do not want to modify it.
1038 * We add (void) to let the compiler know that we do not care
1039 * about the return value of these functions. We use the
1040 * cmpxchg to only update if an interrupt did not already
1041 * do it for us. If the cmpxchg fails, we don't care.
1043 (void)local_cmpxchg(&next_page->write, old_write, val);
1044 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1047 * No need to worry about races with clearing out the commit.
1048 * it only can increment when a commit takes place. But that
1049 * only happens in the outer most nested commit.
1051 local_set(&next_page->page->commit, 0);
1053 old_tail = cmpxchg(&cpu_buffer->tail_page,
1054 tail_page, next_page);
1056 if (old_tail == tail_page)
1057 ret = 1;
1060 return ret;
1063 static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1064 struct buffer_page *bpage)
1066 unsigned long val = (unsigned long)bpage;
1068 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1069 return 1;
1071 return 0;
1075 * rb_check_list - make sure a pointer to a list has the last bits zero
1077 static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1078 struct list_head *list)
1080 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1081 return 1;
1082 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1083 return 1;
1084 return 0;
1088 * rb_check_pages - integrity check of buffer pages
1089 * @cpu_buffer: CPU buffer with pages to test
1091 * As a safety measure we check to make sure the data pages have not
1092 * been corrupted.
1094 static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1096 struct list_head *head = cpu_buffer->pages;
1097 struct buffer_page *bpage, *tmp;
1099 /* Reset the head page if it exists */
1100 if (cpu_buffer->head_page)
1101 rb_set_head_page(cpu_buffer);
1103 rb_head_page_deactivate(cpu_buffer);
1105 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1106 return -1;
1107 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1108 return -1;
1110 if (rb_check_list(cpu_buffer, head))
1111 return -1;
1113 list_for_each_entry_safe(bpage, tmp, head, list) {
1114 if (RB_WARN_ON(cpu_buffer,
1115 bpage->list.next->prev != &bpage->list))
1116 return -1;
1117 if (RB_WARN_ON(cpu_buffer,
1118 bpage->list.prev->next != &bpage->list))
1119 return -1;
1120 if (rb_check_list(cpu_buffer, &bpage->list))
1121 return -1;
1124 rb_head_page_activate(cpu_buffer);
1126 return 0;
1129 static int __rb_allocate_pages(int nr_pages, struct list_head *pages, int cpu)
1131 int i;
1132 struct buffer_page *bpage, *tmp;
1134 for (i = 0; i < nr_pages; i++) {
1135 struct page *page;
1137 * __GFP_NORETRY flag makes sure that the allocation fails
1138 * gracefully without invoking oom-killer and the system is
1139 * not destabilized.
1141 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1142 GFP_KERNEL | __GFP_NORETRY,
1143 cpu_to_node(cpu));
1144 if (!bpage)
1145 goto free_pages;
1147 list_add(&bpage->list, pages);
1149 page = alloc_pages_node(cpu_to_node(cpu),
1150 GFP_KERNEL | __GFP_NORETRY, 0);
1151 if (!page)
1152 goto free_pages;
1153 bpage->page = page_address(page);
1154 rb_init_page(bpage->page);
1157 return 0;
1159 free_pages:
1160 list_for_each_entry_safe(bpage, tmp, pages, list) {
1161 list_del_init(&bpage->list);
1162 free_buffer_page(bpage);
1165 return -ENOMEM;
1168 static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1169 unsigned nr_pages)
1171 LIST_HEAD(pages);
1173 WARN_ON(!nr_pages);
1175 if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1176 return -ENOMEM;
1179 * The ring buffer page list is a circular list that does not
1180 * start and end with a list head. All page list items point to
1181 * other pages.
1183 cpu_buffer->pages = pages.next;
1184 list_del(&pages);
1186 cpu_buffer->nr_pages = nr_pages;
1188 rb_check_pages(cpu_buffer);
1190 return 0;
1193 static struct ring_buffer_per_cpu *
1194 rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu)
1196 struct ring_buffer_per_cpu *cpu_buffer;
1197 struct buffer_page *bpage;
1198 struct page *page;
1199 int ret;
1201 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1202 GFP_KERNEL, cpu_to_node(cpu));
1203 if (!cpu_buffer)
1204 return NULL;
1206 cpu_buffer->cpu = cpu;
1207 cpu_buffer->buffer = buffer;
1208 raw_spin_lock_init(&cpu_buffer->reader_lock);
1209 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1210 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1211 INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1212 init_completion(&cpu_buffer->update_done);
1213 init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1214 init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1215 init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1217 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1218 GFP_KERNEL, cpu_to_node(cpu));
1219 if (!bpage)
1220 goto fail_free_buffer;
1222 rb_check_bpage(cpu_buffer, bpage);
1224 cpu_buffer->reader_page = bpage;
1225 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1226 if (!page)
1227 goto fail_free_reader;
1228 bpage->page = page_address(page);
1229 rb_init_page(bpage->page);
1231 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1232 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1234 ret = rb_allocate_pages(cpu_buffer, nr_pages);
1235 if (ret < 0)
1236 goto fail_free_reader;
1238 cpu_buffer->head_page
1239 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1240 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1242 rb_head_page_activate(cpu_buffer);
1244 return cpu_buffer;
1246 fail_free_reader:
1247 free_buffer_page(cpu_buffer->reader_page);
1249 fail_free_buffer:
1250 kfree(cpu_buffer);
1251 return NULL;
1254 static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1256 struct list_head *head = cpu_buffer->pages;
1257 struct buffer_page *bpage, *tmp;
1259 free_buffer_page(cpu_buffer->reader_page);
1261 rb_head_page_deactivate(cpu_buffer);
1263 if (head) {
1264 list_for_each_entry_safe(bpage, tmp, head, list) {
1265 list_del_init(&bpage->list);
1266 free_buffer_page(bpage);
1268 bpage = list_entry(head, struct buffer_page, list);
1269 free_buffer_page(bpage);
1272 kfree(cpu_buffer);
1275 #ifdef CONFIG_HOTPLUG_CPU
1276 static int rb_cpu_notify(struct notifier_block *self,
1277 unsigned long action, void *hcpu);
1278 #endif
1281 * __ring_buffer_alloc - allocate a new ring_buffer
1282 * @size: the size in bytes per cpu that is needed.
1283 * @flags: attributes to set for the ring buffer.
1285 * Currently the only flag that is available is the RB_FL_OVERWRITE
1286 * flag. This flag means that the buffer will overwrite old data
1287 * when the buffer wraps. If this flag is not set, the buffer will
1288 * drop data when the tail hits the head.
1290 struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1291 struct lock_class_key *key)
1293 struct ring_buffer *buffer;
1294 int bsize;
1295 int cpu, nr_pages;
1297 /* keep it in its own cache line */
1298 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1299 GFP_KERNEL);
1300 if (!buffer)
1301 return NULL;
1303 if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1304 goto fail_free_buffer;
1306 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1307 buffer->flags = flags;
1308 buffer->clock = trace_clock_local;
1309 buffer->reader_lock_key = key;
1311 init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1312 init_waitqueue_head(&buffer->irq_work.waiters);
1314 /* need at least two pages */
1315 if (nr_pages < 2)
1316 nr_pages = 2;
1319 * In case of non-hotplug cpu, if the ring-buffer is allocated
1320 * in early initcall, it will not be notified of secondary cpus.
1321 * In that off case, we need to allocate for all possible cpus.
1323 #ifdef CONFIG_HOTPLUG_CPU
1324 cpu_notifier_register_begin();
1325 cpumask_copy(buffer->cpumask, cpu_online_mask);
1326 #else
1327 cpumask_copy(buffer->cpumask, cpu_possible_mask);
1328 #endif
1329 buffer->cpus = nr_cpu_ids;
1331 bsize = sizeof(void *) * nr_cpu_ids;
1332 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1333 GFP_KERNEL);
1334 if (!buffer->buffers)
1335 goto fail_free_cpumask;
1337 for_each_buffer_cpu(buffer, cpu) {
1338 buffer->buffers[cpu] =
1339 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1340 if (!buffer->buffers[cpu])
1341 goto fail_free_buffers;
1344 #ifdef CONFIG_HOTPLUG_CPU
1345 buffer->cpu_notify.notifier_call = rb_cpu_notify;
1346 buffer->cpu_notify.priority = 0;
1347 __register_cpu_notifier(&buffer->cpu_notify);
1348 cpu_notifier_register_done();
1349 #endif
1351 mutex_init(&buffer->mutex);
1353 return buffer;
1355 fail_free_buffers:
1356 for_each_buffer_cpu(buffer, cpu) {
1357 if (buffer->buffers[cpu])
1358 rb_free_cpu_buffer(buffer->buffers[cpu]);
1360 kfree(buffer->buffers);
1362 fail_free_cpumask:
1363 free_cpumask_var(buffer->cpumask);
1364 #ifdef CONFIG_HOTPLUG_CPU
1365 cpu_notifier_register_done();
1366 #endif
1368 fail_free_buffer:
1369 kfree(buffer);
1370 return NULL;
1372 EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1375 * ring_buffer_free - free a ring buffer.
1376 * @buffer: the buffer to free.
1378 void
1379 ring_buffer_free(struct ring_buffer *buffer)
1381 int cpu;
1383 #ifdef CONFIG_HOTPLUG_CPU
1384 cpu_notifier_register_begin();
1385 __unregister_cpu_notifier(&buffer->cpu_notify);
1386 #endif
1388 for_each_buffer_cpu(buffer, cpu)
1389 rb_free_cpu_buffer(buffer->buffers[cpu]);
1391 #ifdef CONFIG_HOTPLUG_CPU
1392 cpu_notifier_register_done();
1393 #endif
1395 kfree(buffer->buffers);
1396 free_cpumask_var(buffer->cpumask);
1398 kfree(buffer);
1400 EXPORT_SYMBOL_GPL(ring_buffer_free);
1402 void ring_buffer_set_clock(struct ring_buffer *buffer,
1403 u64 (*clock)(void))
1405 buffer->clock = clock;
1408 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1410 static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1412 return local_read(&bpage->entries) & RB_WRITE_MASK;
1415 static inline unsigned long rb_page_write(struct buffer_page *bpage)
1417 return local_read(&bpage->write) & RB_WRITE_MASK;
1420 static int
1421 rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
1423 struct list_head *tail_page, *to_remove, *next_page;
1424 struct buffer_page *to_remove_page, *tmp_iter_page;
1425 struct buffer_page *last_page, *first_page;
1426 unsigned int nr_removed;
1427 unsigned long head_bit;
1428 int page_entries;
1430 head_bit = 0;
1432 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1433 atomic_inc(&cpu_buffer->record_disabled);
1435 * We don't race with the readers since we have acquired the reader
1436 * lock. We also don't race with writers after disabling recording.
1437 * This makes it easy to figure out the first and the last page to be
1438 * removed from the list. We unlink all the pages in between including
1439 * the first and last pages. This is done in a busy loop so that we
1440 * lose the least number of traces.
1441 * The pages are freed after we restart recording and unlock readers.
1443 tail_page = &cpu_buffer->tail_page->list;
1446 * tail page might be on reader page, we remove the next page
1447 * from the ring buffer
1449 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1450 tail_page = rb_list_head(tail_page->next);
1451 to_remove = tail_page;
1453 /* start of pages to remove */
1454 first_page = list_entry(rb_list_head(to_remove->next),
1455 struct buffer_page, list);
1457 for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1458 to_remove = rb_list_head(to_remove)->next;
1459 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1462 next_page = rb_list_head(to_remove)->next;
1465 * Now we remove all pages between tail_page and next_page.
1466 * Make sure that we have head_bit value preserved for the
1467 * next page
1469 tail_page->next = (struct list_head *)((unsigned long)next_page |
1470 head_bit);
1471 next_page = rb_list_head(next_page);
1472 next_page->prev = tail_page;
1474 /* make sure pages points to a valid page in the ring buffer */
1475 cpu_buffer->pages = next_page;
1477 /* update head page */
1478 if (head_bit)
1479 cpu_buffer->head_page = list_entry(next_page,
1480 struct buffer_page, list);
1483 * change read pointer to make sure any read iterators reset
1484 * themselves
1486 cpu_buffer->read = 0;
1488 /* pages are removed, resume tracing and then free the pages */
1489 atomic_dec(&cpu_buffer->record_disabled);
1490 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1492 RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1494 /* last buffer page to remove */
1495 last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1496 list);
1497 tmp_iter_page = first_page;
1499 do {
1500 to_remove_page = tmp_iter_page;
1501 rb_inc_page(cpu_buffer, &tmp_iter_page);
1503 /* update the counters */
1504 page_entries = rb_page_entries(to_remove_page);
1505 if (page_entries) {
1507 * If something was added to this page, it was full
1508 * since it is not the tail page. So we deduct the
1509 * bytes consumed in ring buffer from here.
1510 * Increment overrun to account for the lost events.
1512 local_add(page_entries, &cpu_buffer->overrun);
1513 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1517 * We have already removed references to this list item, just
1518 * free up the buffer_page and its page
1520 free_buffer_page(to_remove_page);
1521 nr_removed--;
1523 } while (to_remove_page != last_page);
1525 RB_WARN_ON(cpu_buffer, nr_removed);
1527 return nr_removed == 0;
1530 static int
1531 rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1533 struct list_head *pages = &cpu_buffer->new_pages;
1534 int retries, success;
1536 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1538 * We are holding the reader lock, so the reader page won't be swapped
1539 * in the ring buffer. Now we are racing with the writer trying to
1540 * move head page and the tail page.
1541 * We are going to adapt the reader page update process where:
1542 * 1. We first splice the start and end of list of new pages between
1543 * the head page and its previous page.
1544 * 2. We cmpxchg the prev_page->next to point from head page to the
1545 * start of new pages list.
1546 * 3. Finally, we update the head->prev to the end of new list.
1548 * We will try this process 10 times, to make sure that we don't keep
1549 * spinning.
1551 retries = 10;
1552 success = 0;
1553 while (retries--) {
1554 struct list_head *head_page, *prev_page, *r;
1555 struct list_head *last_page, *first_page;
1556 struct list_head *head_page_with_bit;
1558 head_page = &rb_set_head_page(cpu_buffer)->list;
1559 if (!head_page)
1560 break;
1561 prev_page = head_page->prev;
1563 first_page = pages->next;
1564 last_page = pages->prev;
1566 head_page_with_bit = (struct list_head *)
1567 ((unsigned long)head_page | RB_PAGE_HEAD);
1569 last_page->next = head_page_with_bit;
1570 first_page->prev = prev_page;
1572 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1574 if (r == head_page_with_bit) {
1576 * yay, we replaced the page pointer to our new list,
1577 * now, we just have to update to head page's prev
1578 * pointer to point to end of list
1580 head_page->prev = last_page;
1581 success = 1;
1582 break;
1586 if (success)
1587 INIT_LIST_HEAD(pages);
1589 * If we weren't successful in adding in new pages, warn and stop
1590 * tracing
1592 RB_WARN_ON(cpu_buffer, !success);
1593 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1595 /* free pages if they weren't inserted */
1596 if (!success) {
1597 struct buffer_page *bpage, *tmp;
1598 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1599 list) {
1600 list_del_init(&bpage->list);
1601 free_buffer_page(bpage);
1604 return success;
1607 static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1609 int success;
1611 if (cpu_buffer->nr_pages_to_update > 0)
1612 success = rb_insert_pages(cpu_buffer);
1613 else
1614 success = rb_remove_pages(cpu_buffer,
1615 -cpu_buffer->nr_pages_to_update);
1617 if (success)
1618 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1621 static void update_pages_handler(struct work_struct *work)
1623 struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1624 struct ring_buffer_per_cpu, update_pages_work);
1625 rb_update_pages(cpu_buffer);
1626 complete(&cpu_buffer->update_done);
1630 * ring_buffer_resize - resize the ring buffer
1631 * @buffer: the buffer to resize.
1632 * @size: the new size.
1633 * @cpu_id: the cpu buffer to resize
1635 * Minimum size is 2 * BUF_PAGE_SIZE.
1637 * Returns 0 on success and < 0 on failure.
1639 int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1640 int cpu_id)
1642 struct ring_buffer_per_cpu *cpu_buffer;
1643 unsigned nr_pages;
1644 int cpu, err = 0;
1647 * Always succeed at resizing a non-existent buffer:
1649 if (!buffer)
1650 return size;
1652 /* Make sure the requested buffer exists */
1653 if (cpu_id != RING_BUFFER_ALL_CPUS &&
1654 !cpumask_test_cpu(cpu_id, buffer->cpumask))
1655 return size;
1657 size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1658 size *= BUF_PAGE_SIZE;
1660 /* we need a minimum of two pages */
1661 if (size < BUF_PAGE_SIZE * 2)
1662 size = BUF_PAGE_SIZE * 2;
1664 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1667 * Don't succeed if resizing is disabled, as a reader might be
1668 * manipulating the ring buffer and is expecting a sane state while
1669 * this is true.
1671 if (atomic_read(&buffer->resize_disabled))
1672 return -EBUSY;
1674 /* prevent another thread from changing buffer sizes */
1675 mutex_lock(&buffer->mutex);
1677 if (cpu_id == RING_BUFFER_ALL_CPUS) {
1678 /* calculate the pages to update */
1679 for_each_buffer_cpu(buffer, cpu) {
1680 cpu_buffer = buffer->buffers[cpu];
1682 cpu_buffer->nr_pages_to_update = nr_pages -
1683 cpu_buffer->nr_pages;
1685 * nothing more to do for removing pages or no update
1687 if (cpu_buffer->nr_pages_to_update <= 0)
1688 continue;
1690 * to add pages, make sure all new pages can be
1691 * allocated without receiving ENOMEM
1693 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1694 if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1695 &cpu_buffer->new_pages, cpu)) {
1696 /* not enough memory for new pages */
1697 err = -ENOMEM;
1698 goto out_err;
1702 get_online_cpus();
1704 * Fire off all the required work handlers
1705 * We can't schedule on offline CPUs, but it's not necessary
1706 * since we can change their buffer sizes without any race.
1708 for_each_buffer_cpu(buffer, cpu) {
1709 cpu_buffer = buffer->buffers[cpu];
1710 if (!cpu_buffer->nr_pages_to_update)
1711 continue;
1713 /* Can't run something on an offline CPU. */
1714 if (!cpu_online(cpu)) {
1715 rb_update_pages(cpu_buffer);
1716 cpu_buffer->nr_pages_to_update = 0;
1717 } else {
1718 schedule_work_on(cpu,
1719 &cpu_buffer->update_pages_work);
1723 /* wait for all the updates to complete */
1724 for_each_buffer_cpu(buffer, cpu) {
1725 cpu_buffer = buffer->buffers[cpu];
1726 if (!cpu_buffer->nr_pages_to_update)
1727 continue;
1729 if (cpu_online(cpu))
1730 wait_for_completion(&cpu_buffer->update_done);
1731 cpu_buffer->nr_pages_to_update = 0;
1734 put_online_cpus();
1735 } else {
1736 /* Make sure this CPU has been intitialized */
1737 if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
1738 goto out;
1740 cpu_buffer = buffer->buffers[cpu_id];
1742 if (nr_pages == cpu_buffer->nr_pages)
1743 goto out;
1745 cpu_buffer->nr_pages_to_update = nr_pages -
1746 cpu_buffer->nr_pages;
1748 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1749 if (cpu_buffer->nr_pages_to_update > 0 &&
1750 __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1751 &cpu_buffer->new_pages, cpu_id)) {
1752 err = -ENOMEM;
1753 goto out_err;
1756 get_online_cpus();
1758 /* Can't run something on an offline CPU. */
1759 if (!cpu_online(cpu_id))
1760 rb_update_pages(cpu_buffer);
1761 else {
1762 schedule_work_on(cpu_id,
1763 &cpu_buffer->update_pages_work);
1764 wait_for_completion(&cpu_buffer->update_done);
1767 cpu_buffer->nr_pages_to_update = 0;
1768 put_online_cpus();
1771 out:
1773 * The ring buffer resize can happen with the ring buffer
1774 * enabled, so that the update disturbs the tracing as little
1775 * as possible. But if the buffer is disabled, we do not need
1776 * to worry about that, and we can take the time to verify
1777 * that the buffer is not corrupt.
1779 if (atomic_read(&buffer->record_disabled)) {
1780 atomic_inc(&buffer->record_disabled);
1782 * Even though the buffer was disabled, we must make sure
1783 * that it is truly disabled before calling rb_check_pages.
1784 * There could have been a race between checking
1785 * record_disable and incrementing it.
1787 synchronize_sched();
1788 for_each_buffer_cpu(buffer, cpu) {
1789 cpu_buffer = buffer->buffers[cpu];
1790 rb_check_pages(cpu_buffer);
1792 atomic_dec(&buffer->record_disabled);
1795 mutex_unlock(&buffer->mutex);
1796 return size;
1798 out_err:
1799 for_each_buffer_cpu(buffer, cpu) {
1800 struct buffer_page *bpage, *tmp;
1802 cpu_buffer = buffer->buffers[cpu];
1803 cpu_buffer->nr_pages_to_update = 0;
1805 if (list_empty(&cpu_buffer->new_pages))
1806 continue;
1808 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1809 list) {
1810 list_del_init(&bpage->list);
1811 free_buffer_page(bpage);
1814 mutex_unlock(&buffer->mutex);
1815 return err;
1817 EXPORT_SYMBOL_GPL(ring_buffer_resize);
1819 void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1821 mutex_lock(&buffer->mutex);
1822 if (val)
1823 buffer->flags |= RB_FL_OVERWRITE;
1824 else
1825 buffer->flags &= ~RB_FL_OVERWRITE;
1826 mutex_unlock(&buffer->mutex);
1828 EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1830 static inline void *
1831 __rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
1833 return bpage->data + index;
1836 static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1838 return bpage->page->data + index;
1841 static inline struct ring_buffer_event *
1842 rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1844 return __rb_page_index(cpu_buffer->reader_page,
1845 cpu_buffer->reader_page->read);
1848 static inline struct ring_buffer_event *
1849 rb_iter_head_event(struct ring_buffer_iter *iter)
1851 return __rb_page_index(iter->head_page, iter->head);
1854 static inline unsigned rb_page_commit(struct buffer_page *bpage)
1856 return local_read(&bpage->page->commit);
1859 /* Size is determined by what has been committed */
1860 static inline unsigned rb_page_size(struct buffer_page *bpage)
1862 return rb_page_commit(bpage);
1865 static inline unsigned
1866 rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1868 return rb_page_commit(cpu_buffer->commit_page);
1871 static inline unsigned
1872 rb_event_index(struct ring_buffer_event *event)
1874 unsigned long addr = (unsigned long)event;
1876 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1879 static inline int
1880 rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
1881 struct ring_buffer_event *event)
1883 unsigned long addr = (unsigned long)event;
1884 unsigned long index;
1886 index = rb_event_index(event);
1887 addr &= PAGE_MASK;
1889 return cpu_buffer->commit_page->page == (void *)addr &&
1890 rb_commit_index(cpu_buffer) == index;
1893 static void
1894 rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
1896 unsigned long max_count;
1899 * We only race with interrupts and NMIs on this CPU.
1900 * If we own the commit event, then we can commit
1901 * all others that interrupted us, since the interruptions
1902 * are in stack format (they finish before they come
1903 * back to us). This allows us to do a simple loop to
1904 * assign the commit to the tail.
1906 again:
1907 max_count = cpu_buffer->nr_pages * 100;
1909 while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
1910 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
1911 return;
1912 if (RB_WARN_ON(cpu_buffer,
1913 rb_is_reader_page(cpu_buffer->tail_page)))
1914 return;
1915 local_set(&cpu_buffer->commit_page->page->commit,
1916 rb_page_write(cpu_buffer->commit_page));
1917 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
1918 cpu_buffer->write_stamp =
1919 cpu_buffer->commit_page->page->time_stamp;
1920 /* add barrier to keep gcc from optimizing too much */
1921 barrier();
1923 while (rb_commit_index(cpu_buffer) !=
1924 rb_page_write(cpu_buffer->commit_page)) {
1926 local_set(&cpu_buffer->commit_page->page->commit,
1927 rb_page_write(cpu_buffer->commit_page));
1928 RB_WARN_ON(cpu_buffer,
1929 local_read(&cpu_buffer->commit_page->page->commit) &
1930 ~RB_WRITE_MASK);
1931 barrier();
1934 /* again, keep gcc from optimizing */
1935 barrier();
1938 * If an interrupt came in just after the first while loop
1939 * and pushed the tail page forward, we will be left with
1940 * a dangling commit that will never go forward.
1942 if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
1943 goto again;
1946 static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
1948 cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
1949 cpu_buffer->reader_page->read = 0;
1952 static void rb_inc_iter(struct ring_buffer_iter *iter)
1954 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1957 * The iterator could be on the reader page (it starts there).
1958 * But the head could have moved, since the reader was
1959 * found. Check for this case and assign the iterator
1960 * to the head page instead of next.
1962 if (iter->head_page == cpu_buffer->reader_page)
1963 iter->head_page = rb_set_head_page(cpu_buffer);
1964 else
1965 rb_inc_page(cpu_buffer, &iter->head_page);
1967 iter->read_stamp = iter->head_page->page->time_stamp;
1968 iter->head = 0;
1971 /* Slow path, do not inline */
1972 static noinline struct ring_buffer_event *
1973 rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
1975 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
1977 /* Not the first event on the page? */
1978 if (rb_event_index(event)) {
1979 event->time_delta = delta & TS_MASK;
1980 event->array[0] = delta >> TS_SHIFT;
1981 } else {
1982 /* nope, just zero it */
1983 event->time_delta = 0;
1984 event->array[0] = 0;
1987 return skip_time_extend(event);
1991 * rb_update_event - update event type and data
1992 * @event: the event to update
1993 * @type: the type of event
1994 * @length: the size of the event field in the ring buffer
1996 * Update the type and data fields of the event. The length
1997 * is the actual size that is written to the ring buffer,
1998 * and with this, we can determine what to place into the
1999 * data field.
2001 static void
2002 rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2003 struct ring_buffer_event *event, unsigned length,
2004 int add_timestamp, u64 delta)
2006 /* Only a commit updates the timestamp */
2007 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
2008 delta = 0;
2011 * If we need to add a timestamp, then we
2012 * add it to the start of the resevered space.
2014 if (unlikely(add_timestamp)) {
2015 event = rb_add_time_stamp(event, delta);
2016 length -= RB_LEN_TIME_EXTEND;
2017 delta = 0;
2020 event->time_delta = delta;
2021 length -= RB_EVNT_HDR_SIZE;
2022 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2023 event->type_len = 0;
2024 event->array[0] = length;
2025 } else
2026 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2030 * rb_handle_head_page - writer hit the head page
2032 * Returns: +1 to retry page
2033 * 0 to continue
2034 * -1 on error
2036 static int
2037 rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
2038 struct buffer_page *tail_page,
2039 struct buffer_page *next_page)
2041 struct buffer_page *new_head;
2042 int entries;
2043 int type;
2044 int ret;
2046 entries = rb_page_entries(next_page);
2049 * The hard part is here. We need to move the head
2050 * forward, and protect against both readers on
2051 * other CPUs and writers coming in via interrupts.
2053 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
2054 RB_PAGE_HEAD);
2057 * type can be one of four:
2058 * NORMAL - an interrupt already moved it for us
2059 * HEAD - we are the first to get here.
2060 * UPDATE - we are the interrupt interrupting
2061 * a current move.
2062 * MOVED - a reader on another CPU moved the next
2063 * pointer to its reader page. Give up
2064 * and try again.
2067 switch (type) {
2068 case RB_PAGE_HEAD:
2070 * We changed the head to UPDATE, thus
2071 * it is our responsibility to update
2072 * the counters.
2074 local_add(entries, &cpu_buffer->overrun);
2075 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
2078 * The entries will be zeroed out when we move the
2079 * tail page.
2082 /* still more to do */
2083 break;
2085 case RB_PAGE_UPDATE:
2087 * This is an interrupt that interrupt the
2088 * previous update. Still more to do.
2090 break;
2091 case RB_PAGE_NORMAL:
2093 * An interrupt came in before the update
2094 * and processed this for us.
2095 * Nothing left to do.
2097 return 1;
2098 case RB_PAGE_MOVED:
2100 * The reader is on another CPU and just did
2101 * a swap with our next_page.
2102 * Try again.
2104 return 1;
2105 default:
2106 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
2107 return -1;
2111 * Now that we are here, the old head pointer is
2112 * set to UPDATE. This will keep the reader from
2113 * swapping the head page with the reader page.
2114 * The reader (on another CPU) will spin till
2115 * we are finished.
2117 * We just need to protect against interrupts
2118 * doing the job. We will set the next pointer
2119 * to HEAD. After that, we set the old pointer
2120 * to NORMAL, but only if it was HEAD before.
2121 * otherwise we are an interrupt, and only
2122 * want the outer most commit to reset it.
2124 new_head = next_page;
2125 rb_inc_page(cpu_buffer, &new_head);
2127 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2128 RB_PAGE_NORMAL);
2131 * Valid returns are:
2132 * HEAD - an interrupt came in and already set it.
2133 * NORMAL - One of two things:
2134 * 1) We really set it.
2135 * 2) A bunch of interrupts came in and moved
2136 * the page forward again.
2138 switch (ret) {
2139 case RB_PAGE_HEAD:
2140 case RB_PAGE_NORMAL:
2141 /* OK */
2142 break;
2143 default:
2144 RB_WARN_ON(cpu_buffer, 1);
2145 return -1;
2149 * It is possible that an interrupt came in,
2150 * set the head up, then more interrupts came in
2151 * and moved it again. When we get back here,
2152 * the page would have been set to NORMAL but we
2153 * just set it back to HEAD.
2155 * How do you detect this? Well, if that happened
2156 * the tail page would have moved.
2158 if (ret == RB_PAGE_NORMAL) {
2160 * If the tail had moved passed next, then we need
2161 * to reset the pointer.
2163 if (cpu_buffer->tail_page != tail_page &&
2164 cpu_buffer->tail_page != next_page)
2165 rb_head_page_set_normal(cpu_buffer, new_head,
2166 next_page,
2167 RB_PAGE_HEAD);
2171 * If this was the outer most commit (the one that
2172 * changed the original pointer from HEAD to UPDATE),
2173 * then it is up to us to reset it to NORMAL.
2175 if (type == RB_PAGE_HEAD) {
2176 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2177 tail_page,
2178 RB_PAGE_UPDATE);
2179 if (RB_WARN_ON(cpu_buffer,
2180 ret != RB_PAGE_UPDATE))
2181 return -1;
2184 return 0;
2187 static unsigned rb_calculate_event_length(unsigned length)
2189 struct ring_buffer_event event; /* Used only for sizeof array */
2191 /* zero length can cause confusions */
2192 if (!length)
2193 length++;
2195 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2196 length += sizeof(event.array[0]);
2198 length += RB_EVNT_HDR_SIZE;
2199 length = ALIGN(length, RB_ARCH_ALIGNMENT);
2201 return length;
2204 static inline void
2205 rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2206 struct buffer_page *tail_page,
2207 unsigned long tail, unsigned long length)
2209 struct ring_buffer_event *event;
2212 * Only the event that crossed the page boundary
2213 * must fill the old tail_page with padding.
2215 if (tail >= BUF_PAGE_SIZE) {
2217 * If the page was filled, then we still need
2218 * to update the real_end. Reset it to zero
2219 * and the reader will ignore it.
2221 if (tail == BUF_PAGE_SIZE)
2222 tail_page->real_end = 0;
2224 local_sub(length, &tail_page->write);
2225 return;
2228 event = __rb_page_index(tail_page, tail);
2229 kmemcheck_annotate_bitfield(event, bitfield);
2231 /* account for padding bytes */
2232 local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2235 * Save the original length to the meta data.
2236 * This will be used by the reader to add lost event
2237 * counter.
2239 tail_page->real_end = tail;
2242 * If this event is bigger than the minimum size, then
2243 * we need to be careful that we don't subtract the
2244 * write counter enough to allow another writer to slip
2245 * in on this page.
2246 * We put in a discarded commit instead, to make sure
2247 * that this space is not used again.
2249 * If we are less than the minimum size, we don't need to
2250 * worry about it.
2252 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2253 /* No room for any events */
2255 /* Mark the rest of the page with padding */
2256 rb_event_set_padding(event);
2258 /* Set the write back to the previous setting */
2259 local_sub(length, &tail_page->write);
2260 return;
2263 /* Put in a discarded event */
2264 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2265 event->type_len = RINGBUF_TYPE_PADDING;
2266 /* time delta must be non zero */
2267 event->time_delta = 1;
2269 /* Set write to end of buffer */
2270 length = (tail + length) - BUF_PAGE_SIZE;
2271 local_sub(length, &tail_page->write);
2275 * This is the slow path, force gcc not to inline it.
2277 static noinline struct ring_buffer_event *
2278 rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2279 unsigned long length, unsigned long tail,
2280 struct buffer_page *tail_page, u64 ts)
2282 struct buffer_page *commit_page = cpu_buffer->commit_page;
2283 struct ring_buffer *buffer = cpu_buffer->buffer;
2284 struct buffer_page *next_page;
2285 int ret;
2287 next_page = tail_page;
2289 rb_inc_page(cpu_buffer, &next_page);
2292 * If for some reason, we had an interrupt storm that made
2293 * it all the way around the buffer, bail, and warn
2294 * about it.
2296 if (unlikely(next_page == commit_page)) {
2297 local_inc(&cpu_buffer->commit_overrun);
2298 goto out_reset;
2302 * This is where the fun begins!
2304 * We are fighting against races between a reader that
2305 * could be on another CPU trying to swap its reader
2306 * page with the buffer head.
2308 * We are also fighting against interrupts coming in and
2309 * moving the head or tail on us as well.
2311 * If the next page is the head page then we have filled
2312 * the buffer, unless the commit page is still on the
2313 * reader page.
2315 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2318 * If the commit is not on the reader page, then
2319 * move the header page.
2321 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2323 * If we are not in overwrite mode,
2324 * this is easy, just stop here.
2326 if (!(buffer->flags & RB_FL_OVERWRITE)) {
2327 local_inc(&cpu_buffer->dropped_events);
2328 goto out_reset;
2331 ret = rb_handle_head_page(cpu_buffer,
2332 tail_page,
2333 next_page);
2334 if (ret < 0)
2335 goto out_reset;
2336 if (ret)
2337 goto out_again;
2338 } else {
2340 * We need to be careful here too. The
2341 * commit page could still be on the reader
2342 * page. We could have a small buffer, and
2343 * have filled up the buffer with events
2344 * from interrupts and such, and wrapped.
2346 * Note, if the tail page is also the on the
2347 * reader_page, we let it move out.
2349 if (unlikely((cpu_buffer->commit_page !=
2350 cpu_buffer->tail_page) &&
2351 (cpu_buffer->commit_page ==
2352 cpu_buffer->reader_page))) {
2353 local_inc(&cpu_buffer->commit_overrun);
2354 goto out_reset;
2359 ret = rb_tail_page_update(cpu_buffer, tail_page, next_page);
2360 if (ret) {
2362 * Nested commits always have zero deltas, so
2363 * just reread the time stamp
2365 ts = rb_time_stamp(buffer);
2366 next_page->page->time_stamp = ts;
2369 out_again:
2371 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2373 /* fail and let the caller try again */
2374 return ERR_PTR(-EAGAIN);
2376 out_reset:
2377 /* reset write */
2378 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2380 return NULL;
2383 static struct ring_buffer_event *
2384 __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2385 unsigned long length, u64 ts,
2386 u64 delta, int add_timestamp)
2388 struct buffer_page *tail_page;
2389 struct ring_buffer_event *event;
2390 unsigned long tail, write;
2393 * If the time delta since the last event is too big to
2394 * hold in the time field of the event, then we append a
2395 * TIME EXTEND event ahead of the data event.
2397 if (unlikely(add_timestamp))
2398 length += RB_LEN_TIME_EXTEND;
2400 tail_page = cpu_buffer->tail_page;
2401 write = local_add_return(length, &tail_page->write);
2403 /* set write to only the index of the write */
2404 write &= RB_WRITE_MASK;
2405 tail = write - length;
2408 * If this is the first commit on the page, then it has the same
2409 * timestamp as the page itself.
2411 if (!tail)
2412 delta = 0;
2414 /* See if we shot pass the end of this buffer page */
2415 if (unlikely(write > BUF_PAGE_SIZE))
2416 return rb_move_tail(cpu_buffer, length, tail,
2417 tail_page, ts);
2419 /* We reserved something on the buffer */
2421 event = __rb_page_index(tail_page, tail);
2422 kmemcheck_annotate_bitfield(event, bitfield);
2423 rb_update_event(cpu_buffer, event, length, add_timestamp, delta);
2425 local_inc(&tail_page->entries);
2428 * If this is the first commit on the page, then update
2429 * its timestamp.
2431 if (!tail)
2432 tail_page->page->time_stamp = ts;
2434 /* account for these added bytes */
2435 local_add(length, &cpu_buffer->entries_bytes);
2437 return event;
2440 static inline int
2441 rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2442 struct ring_buffer_event *event)
2444 unsigned long new_index, old_index;
2445 struct buffer_page *bpage;
2446 unsigned long index;
2447 unsigned long addr;
2449 new_index = rb_event_index(event);
2450 old_index = new_index + rb_event_ts_length(event);
2451 addr = (unsigned long)event;
2452 addr &= PAGE_MASK;
2454 bpage = cpu_buffer->tail_page;
2456 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2457 unsigned long write_mask =
2458 local_read(&bpage->write) & ~RB_WRITE_MASK;
2459 unsigned long event_length = rb_event_length(event);
2461 * This is on the tail page. It is possible that
2462 * a write could come in and move the tail page
2463 * and write to the next page. That is fine
2464 * because we just shorten what is on this page.
2466 old_index += write_mask;
2467 new_index += write_mask;
2468 index = local_cmpxchg(&bpage->write, old_index, new_index);
2469 if (index == old_index) {
2470 /* update counters */
2471 local_sub(event_length, &cpu_buffer->entries_bytes);
2472 return 1;
2476 /* could not discard */
2477 return 0;
2480 static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2482 local_inc(&cpu_buffer->committing);
2483 local_inc(&cpu_buffer->commits);
2486 static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2488 unsigned long commits;
2490 if (RB_WARN_ON(cpu_buffer,
2491 !local_read(&cpu_buffer->committing)))
2492 return;
2494 again:
2495 commits = local_read(&cpu_buffer->commits);
2496 /* synchronize with interrupts */
2497 barrier();
2498 if (local_read(&cpu_buffer->committing) == 1)
2499 rb_set_commit_to_write(cpu_buffer);
2501 local_dec(&cpu_buffer->committing);
2503 /* synchronize with interrupts */
2504 barrier();
2507 * Need to account for interrupts coming in between the
2508 * updating of the commit page and the clearing of the
2509 * committing counter.
2511 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2512 !local_read(&cpu_buffer->committing)) {
2513 local_inc(&cpu_buffer->committing);
2514 goto again;
2518 static struct ring_buffer_event *
2519 rb_reserve_next_event(struct ring_buffer *buffer,
2520 struct ring_buffer_per_cpu *cpu_buffer,
2521 unsigned long length)
2523 struct ring_buffer_event *event;
2524 u64 ts, delta;
2525 int nr_loops = 0;
2526 int add_timestamp;
2527 u64 diff;
2529 rb_start_commit(cpu_buffer);
2531 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2533 * Due to the ability to swap a cpu buffer from a buffer
2534 * it is possible it was swapped before we committed.
2535 * (committing stops a swap). We check for it here and
2536 * if it happened, we have to fail the write.
2538 barrier();
2539 if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
2540 local_dec(&cpu_buffer->committing);
2541 local_dec(&cpu_buffer->commits);
2542 return NULL;
2544 #endif
2546 length = rb_calculate_event_length(length);
2547 again:
2548 add_timestamp = 0;
2549 delta = 0;
2552 * We allow for interrupts to reenter here and do a trace.
2553 * If one does, it will cause this original code to loop
2554 * back here. Even with heavy interrupts happening, this
2555 * should only happen a few times in a row. If this happens
2556 * 1000 times in a row, there must be either an interrupt
2557 * storm or we have something buggy.
2558 * Bail!
2560 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2561 goto out_fail;
2563 ts = rb_time_stamp(cpu_buffer->buffer);
2564 diff = ts - cpu_buffer->write_stamp;
2566 /* make sure this diff is calculated here */
2567 barrier();
2569 /* Did the write stamp get updated already? */
2570 if (likely(ts >= cpu_buffer->write_stamp)) {
2571 delta = diff;
2572 if (unlikely(test_time_stamp(delta))) {
2573 int local_clock_stable = 1;
2574 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2575 local_clock_stable = sched_clock_stable();
2576 #endif
2577 WARN_ONCE(delta > (1ULL << 59),
2578 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2579 (unsigned long long)delta,
2580 (unsigned long long)ts,
2581 (unsigned long long)cpu_buffer->write_stamp,
2582 local_clock_stable ? "" :
2583 "If you just came from a suspend/resume,\n"
2584 "please switch to the trace global clock:\n"
2585 " echo global > /sys/kernel/debug/tracing/trace_clock\n");
2586 add_timestamp = 1;
2590 event = __rb_reserve_next(cpu_buffer, length, ts,
2591 delta, add_timestamp);
2592 if (unlikely(PTR_ERR(event) == -EAGAIN))
2593 goto again;
2595 if (!event)
2596 goto out_fail;
2598 return event;
2600 out_fail:
2601 rb_end_commit(cpu_buffer);
2602 return NULL;
2606 * The lock and unlock are done within a preempt disable section.
2607 * The current_context per_cpu variable can only be modified
2608 * by the current task between lock and unlock. But it can
2609 * be modified more than once via an interrupt. To pass this
2610 * information from the lock to the unlock without having to
2611 * access the 'in_interrupt()' functions again (which do show
2612 * a bit of overhead in something as critical as function tracing,
2613 * we use a bitmask trick.
2615 * bit 0 = NMI context
2616 * bit 1 = IRQ context
2617 * bit 2 = SoftIRQ context
2618 * bit 3 = normal context.
2620 * This works because this is the order of contexts that can
2621 * preempt other contexts. A SoftIRQ never preempts an IRQ
2622 * context.
2624 * When the context is determined, the corresponding bit is
2625 * checked and set (if it was set, then a recursion of that context
2626 * happened).
2628 * On unlock, we need to clear this bit. To do so, just subtract
2629 * 1 from the current_context and AND it to itself.
2631 * (binary)
2632 * 101 - 1 = 100
2633 * 101 & 100 = 100 (clearing bit zero)
2635 * 1010 - 1 = 1001
2636 * 1010 & 1001 = 1000 (clearing bit 1)
2638 * The least significant bit can be cleared this way, and it
2639 * just so happens that it is the same bit corresponding to
2640 * the current context.
2643 static __always_inline int
2644 trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
2646 unsigned int val = cpu_buffer->current_context;
2647 int bit;
2649 if (in_interrupt()) {
2650 if (in_nmi())
2651 bit = RB_CTX_NMI;
2652 else if (in_irq())
2653 bit = RB_CTX_IRQ;
2654 else
2655 bit = RB_CTX_SOFTIRQ;
2656 } else
2657 bit = RB_CTX_NORMAL;
2659 if (unlikely(val & (1 << bit)))
2660 return 1;
2662 val |= (1 << bit);
2663 cpu_buffer->current_context = val;
2665 return 0;
2668 static __always_inline void
2669 trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
2671 cpu_buffer->current_context &= cpu_buffer->current_context - 1;
2675 * ring_buffer_lock_reserve - reserve a part of the buffer
2676 * @buffer: the ring buffer to reserve from
2677 * @length: the length of the data to reserve (excluding event header)
2679 * Returns a reseverd event on the ring buffer to copy directly to.
2680 * The user of this interface will need to get the body to write into
2681 * and can use the ring_buffer_event_data() interface.
2683 * The length is the length of the data needed, not the event length
2684 * which also includes the event header.
2686 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2687 * If NULL is returned, then nothing has been allocated or locked.
2689 struct ring_buffer_event *
2690 ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2692 struct ring_buffer_per_cpu *cpu_buffer;
2693 struct ring_buffer_event *event;
2694 int cpu;
2696 /* If we are tracing schedule, we don't want to recurse */
2697 preempt_disable_notrace();
2699 if (unlikely(atomic_read(&buffer->record_disabled)))
2700 goto out;
2702 cpu = raw_smp_processor_id();
2704 if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
2705 goto out;
2707 cpu_buffer = buffer->buffers[cpu];
2709 if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
2710 goto out;
2712 if (unlikely(length > BUF_MAX_DATA_SIZE))
2713 goto out;
2715 if (unlikely(trace_recursive_lock(cpu_buffer)))
2716 goto out;
2718 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2719 if (!event)
2720 goto out_unlock;
2722 return event;
2724 out_unlock:
2725 trace_recursive_unlock(cpu_buffer);
2726 out:
2727 preempt_enable_notrace();
2728 return NULL;
2730 EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
2732 static void
2733 rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2734 struct ring_buffer_event *event)
2736 u64 delta;
2739 * The event first in the commit queue updates the
2740 * time stamp.
2742 if (rb_event_is_commit(cpu_buffer, event)) {
2744 * A commit event that is first on a page
2745 * updates the write timestamp with the page stamp
2747 if (!rb_event_index(event))
2748 cpu_buffer->write_stamp =
2749 cpu_buffer->commit_page->page->time_stamp;
2750 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2751 delta = event->array[0];
2752 delta <<= TS_SHIFT;
2753 delta += event->time_delta;
2754 cpu_buffer->write_stamp += delta;
2755 } else
2756 cpu_buffer->write_stamp += event->time_delta;
2760 static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2761 struct ring_buffer_event *event)
2763 local_inc(&cpu_buffer->entries);
2764 rb_update_write_stamp(cpu_buffer, event);
2765 rb_end_commit(cpu_buffer);
2768 static __always_inline void
2769 rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
2771 bool pagebusy;
2773 if (buffer->irq_work.waiters_pending) {
2774 buffer->irq_work.waiters_pending = false;
2775 /* irq_work_queue() supplies it's own memory barriers */
2776 irq_work_queue(&buffer->irq_work.work);
2779 if (cpu_buffer->irq_work.waiters_pending) {
2780 cpu_buffer->irq_work.waiters_pending = false;
2781 /* irq_work_queue() supplies it's own memory barriers */
2782 irq_work_queue(&cpu_buffer->irq_work.work);
2785 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
2787 if (!pagebusy && cpu_buffer->irq_work.full_waiters_pending) {
2788 cpu_buffer->irq_work.wakeup_full = true;
2789 cpu_buffer->irq_work.full_waiters_pending = false;
2790 /* irq_work_queue() supplies it's own memory barriers */
2791 irq_work_queue(&cpu_buffer->irq_work.work);
2796 * ring_buffer_unlock_commit - commit a reserved
2797 * @buffer: The buffer to commit to
2798 * @event: The event pointer to commit.
2800 * This commits the data to the ring buffer, and releases any locks held.
2802 * Must be paired with ring_buffer_lock_reserve.
2804 int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2805 struct ring_buffer_event *event)
2807 struct ring_buffer_per_cpu *cpu_buffer;
2808 int cpu = raw_smp_processor_id();
2810 cpu_buffer = buffer->buffers[cpu];
2812 rb_commit(cpu_buffer, event);
2814 rb_wakeups(buffer, cpu_buffer);
2816 trace_recursive_unlock(cpu_buffer);
2818 preempt_enable_notrace();
2820 return 0;
2822 EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2824 static inline void rb_event_discard(struct ring_buffer_event *event)
2826 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
2827 event = skip_time_extend(event);
2829 /* array[0] holds the actual length for the discarded event */
2830 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2831 event->type_len = RINGBUF_TYPE_PADDING;
2832 /* time delta must be non zero */
2833 if (!event->time_delta)
2834 event->time_delta = 1;
2838 * Decrement the entries to the page that an event is on.
2839 * The event does not even need to exist, only the pointer
2840 * to the page it is on. This may only be called before the commit
2841 * takes place.
2843 static inline void
2844 rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
2845 struct ring_buffer_event *event)
2847 unsigned long addr = (unsigned long)event;
2848 struct buffer_page *bpage = cpu_buffer->commit_page;
2849 struct buffer_page *start;
2851 addr &= PAGE_MASK;
2853 /* Do the likely case first */
2854 if (likely(bpage->page == (void *)addr)) {
2855 local_dec(&bpage->entries);
2856 return;
2860 * Because the commit page may be on the reader page we
2861 * start with the next page and check the end loop there.
2863 rb_inc_page(cpu_buffer, &bpage);
2864 start = bpage;
2865 do {
2866 if (bpage->page == (void *)addr) {
2867 local_dec(&bpage->entries);
2868 return;
2870 rb_inc_page(cpu_buffer, &bpage);
2871 } while (bpage != start);
2873 /* commit not part of this buffer?? */
2874 RB_WARN_ON(cpu_buffer, 1);
2878 * ring_buffer_commit_discard - discard an event that has not been committed
2879 * @buffer: the ring buffer
2880 * @event: non committed event to discard
2882 * Sometimes an event that is in the ring buffer needs to be ignored.
2883 * This function lets the user discard an event in the ring buffer
2884 * and then that event will not be read later.
2886 * This function only works if it is called before the the item has been
2887 * committed. It will try to free the event from the ring buffer
2888 * if another event has not been added behind it.
2890 * If another event has been added behind it, it will set the event
2891 * up as discarded, and perform the commit.
2893 * If this function is called, do not call ring_buffer_unlock_commit on
2894 * the event.
2896 void ring_buffer_discard_commit(struct ring_buffer *buffer,
2897 struct ring_buffer_event *event)
2899 struct ring_buffer_per_cpu *cpu_buffer;
2900 int cpu;
2902 /* The event is discarded regardless */
2903 rb_event_discard(event);
2905 cpu = smp_processor_id();
2906 cpu_buffer = buffer->buffers[cpu];
2909 * This must only be called if the event has not been
2910 * committed yet. Thus we can assume that preemption
2911 * is still disabled.
2913 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
2915 rb_decrement_entry(cpu_buffer, event);
2916 if (rb_try_to_discard(cpu_buffer, event))
2917 goto out;
2920 * The commit is still visible by the reader, so we
2921 * must still update the timestamp.
2923 rb_update_write_stamp(cpu_buffer, event);
2924 out:
2925 rb_end_commit(cpu_buffer);
2927 trace_recursive_unlock(cpu_buffer);
2929 preempt_enable_notrace();
2932 EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
2935 * ring_buffer_write - write data to the buffer without reserving
2936 * @buffer: The ring buffer to write to.
2937 * @length: The length of the data being written (excluding the event header)
2938 * @data: The data to write to the buffer.
2940 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
2941 * one function. If you already have the data to write to the buffer, it
2942 * may be easier to simply call this function.
2944 * Note, like ring_buffer_lock_reserve, the length is the length of the data
2945 * and not the length of the event which would hold the header.
2947 int ring_buffer_write(struct ring_buffer *buffer,
2948 unsigned long length,
2949 void *data)
2951 struct ring_buffer_per_cpu *cpu_buffer;
2952 struct ring_buffer_event *event;
2953 void *body;
2954 int ret = -EBUSY;
2955 int cpu;
2957 preempt_disable_notrace();
2959 if (atomic_read(&buffer->record_disabled))
2960 goto out;
2962 cpu = raw_smp_processor_id();
2964 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2965 goto out;
2967 cpu_buffer = buffer->buffers[cpu];
2969 if (atomic_read(&cpu_buffer->record_disabled))
2970 goto out;
2972 if (length > BUF_MAX_DATA_SIZE)
2973 goto out;
2975 if (unlikely(trace_recursive_lock(cpu_buffer)))
2976 goto out;
2978 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2979 if (!event)
2980 goto out_unlock;
2982 body = rb_event_data(event);
2984 memcpy(body, data, length);
2986 rb_commit(cpu_buffer, event);
2988 rb_wakeups(buffer, cpu_buffer);
2990 ret = 0;
2992 out_unlock:
2993 trace_recursive_unlock(cpu_buffer);
2995 out:
2996 preempt_enable_notrace();
2998 return ret;
3000 EXPORT_SYMBOL_GPL(ring_buffer_write);
3002 static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3004 struct buffer_page *reader = cpu_buffer->reader_page;
3005 struct buffer_page *head = rb_set_head_page(cpu_buffer);
3006 struct buffer_page *commit = cpu_buffer->commit_page;
3008 /* In case of error, head will be NULL */
3009 if (unlikely(!head))
3010 return 1;
3012 return reader->read == rb_page_commit(reader) &&
3013 (commit == reader ||
3014 (commit == head &&
3015 head->read == rb_page_commit(commit)));
3019 * ring_buffer_record_disable - stop all writes into the buffer
3020 * @buffer: The ring buffer to stop writes to.
3022 * This prevents all writes to the buffer. Any attempt to write
3023 * to the buffer after this will fail and return NULL.
3025 * The caller should call synchronize_sched() after this.
3027 void ring_buffer_record_disable(struct ring_buffer *buffer)
3029 atomic_inc(&buffer->record_disabled);
3031 EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3034 * ring_buffer_record_enable - enable writes to the buffer
3035 * @buffer: The ring buffer to enable writes
3037 * Note, multiple disables will need the same number of enables
3038 * to truly enable the writing (much like preempt_disable).
3040 void ring_buffer_record_enable(struct ring_buffer *buffer)
3042 atomic_dec(&buffer->record_disabled);
3044 EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3047 * ring_buffer_record_off - stop all writes into the buffer
3048 * @buffer: The ring buffer to stop writes to.
3050 * This prevents all writes to the buffer. Any attempt to write
3051 * to the buffer after this will fail and return NULL.
3053 * This is different than ring_buffer_record_disable() as
3054 * it works like an on/off switch, where as the disable() version
3055 * must be paired with a enable().
3057 void ring_buffer_record_off(struct ring_buffer *buffer)
3059 unsigned int rd;
3060 unsigned int new_rd;
3062 do {
3063 rd = atomic_read(&buffer->record_disabled);
3064 new_rd = rd | RB_BUFFER_OFF;
3065 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3067 EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3070 * ring_buffer_record_on - restart writes into the buffer
3071 * @buffer: The ring buffer to start writes to.
3073 * This enables all writes to the buffer that was disabled by
3074 * ring_buffer_record_off().
3076 * This is different than ring_buffer_record_enable() as
3077 * it works like an on/off switch, where as the enable() version
3078 * must be paired with a disable().
3080 void ring_buffer_record_on(struct ring_buffer *buffer)
3082 unsigned int rd;
3083 unsigned int new_rd;
3085 do {
3086 rd = atomic_read(&buffer->record_disabled);
3087 new_rd = rd & ~RB_BUFFER_OFF;
3088 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3090 EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3093 * ring_buffer_record_is_on - return true if the ring buffer can write
3094 * @buffer: The ring buffer to see if write is enabled
3096 * Returns true if the ring buffer is in a state that it accepts writes.
3098 int ring_buffer_record_is_on(struct ring_buffer *buffer)
3100 return !atomic_read(&buffer->record_disabled);
3104 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3105 * @buffer: The ring buffer to stop writes to.
3106 * @cpu: The CPU buffer to stop
3108 * This prevents all writes to the buffer. Any attempt to write
3109 * to the buffer after this will fail and return NULL.
3111 * The caller should call synchronize_sched() after this.
3113 void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
3115 struct ring_buffer_per_cpu *cpu_buffer;
3117 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3118 return;
3120 cpu_buffer = buffer->buffers[cpu];
3121 atomic_inc(&cpu_buffer->record_disabled);
3123 EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
3126 * ring_buffer_record_enable_cpu - enable writes to the buffer
3127 * @buffer: The ring buffer to enable writes
3128 * @cpu: The CPU to enable.
3130 * Note, multiple disables will need the same number of enables
3131 * to truly enable the writing (much like preempt_disable).
3133 void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
3135 struct ring_buffer_per_cpu *cpu_buffer;
3137 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3138 return;
3140 cpu_buffer = buffer->buffers[cpu];
3141 atomic_dec(&cpu_buffer->record_disabled);
3143 EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
3146 * The total entries in the ring buffer is the running counter
3147 * of entries entered into the ring buffer, minus the sum of
3148 * the entries read from the ring buffer and the number of
3149 * entries that were overwritten.
3151 static inline unsigned long
3152 rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
3154 return local_read(&cpu_buffer->entries) -
3155 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
3159 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
3160 * @buffer: The ring buffer
3161 * @cpu: The per CPU buffer to read from.
3163 u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
3165 unsigned long flags;
3166 struct ring_buffer_per_cpu *cpu_buffer;
3167 struct buffer_page *bpage;
3168 u64 ret = 0;
3170 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3171 return 0;
3173 cpu_buffer = buffer->buffers[cpu];
3174 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3176 * if the tail is on reader_page, oldest time stamp is on the reader
3177 * page
3179 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
3180 bpage = cpu_buffer->reader_page;
3181 else
3182 bpage = rb_set_head_page(cpu_buffer);
3183 if (bpage)
3184 ret = bpage->page->time_stamp;
3185 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3187 return ret;
3189 EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
3192 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
3193 * @buffer: The ring buffer
3194 * @cpu: The per CPU buffer to read from.
3196 unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
3198 struct ring_buffer_per_cpu *cpu_buffer;
3199 unsigned long ret;
3201 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3202 return 0;
3204 cpu_buffer = buffer->buffers[cpu];
3205 ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
3207 return ret;
3209 EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
3212 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
3213 * @buffer: The ring buffer
3214 * @cpu: The per CPU buffer to get the entries from.
3216 unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
3218 struct ring_buffer_per_cpu *cpu_buffer;
3220 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3221 return 0;
3223 cpu_buffer = buffer->buffers[cpu];
3225 return rb_num_of_entries(cpu_buffer);
3227 EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
3230 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
3231 * buffer wrapping around (only if RB_FL_OVERWRITE is on).
3232 * @buffer: The ring buffer
3233 * @cpu: The per CPU buffer to get the number of overruns from
3235 unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
3237 struct ring_buffer_per_cpu *cpu_buffer;
3238 unsigned long ret;
3240 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3241 return 0;
3243 cpu_buffer = buffer->buffers[cpu];
3244 ret = local_read(&cpu_buffer->overrun);
3246 return ret;
3248 EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3251 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
3252 * commits failing due to the buffer wrapping around while there are uncommitted
3253 * events, such as during an interrupt storm.
3254 * @buffer: The ring buffer
3255 * @cpu: The per CPU buffer to get the number of overruns from
3257 unsigned long
3258 ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3260 struct ring_buffer_per_cpu *cpu_buffer;
3261 unsigned long ret;
3263 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3264 return 0;
3266 cpu_buffer = buffer->buffers[cpu];
3267 ret = local_read(&cpu_buffer->commit_overrun);
3269 return ret;
3271 EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3274 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
3275 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
3276 * @buffer: The ring buffer
3277 * @cpu: The per CPU buffer to get the number of overruns from
3279 unsigned long
3280 ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
3282 struct ring_buffer_per_cpu *cpu_buffer;
3283 unsigned long ret;
3285 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3286 return 0;
3288 cpu_buffer = buffer->buffers[cpu];
3289 ret = local_read(&cpu_buffer->dropped_events);
3291 return ret;
3293 EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
3296 * ring_buffer_read_events_cpu - get the number of events successfully read
3297 * @buffer: The ring buffer
3298 * @cpu: The per CPU buffer to get the number of events read
3300 unsigned long
3301 ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
3303 struct ring_buffer_per_cpu *cpu_buffer;
3305 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3306 return 0;
3308 cpu_buffer = buffer->buffers[cpu];
3309 return cpu_buffer->read;
3311 EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
3314 * ring_buffer_entries - get the number of entries in a buffer
3315 * @buffer: The ring buffer
3317 * Returns the total number of entries in the ring buffer
3318 * (all CPU entries)
3320 unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3322 struct ring_buffer_per_cpu *cpu_buffer;
3323 unsigned long entries = 0;
3324 int cpu;
3326 /* if you care about this being correct, lock the buffer */
3327 for_each_buffer_cpu(buffer, cpu) {
3328 cpu_buffer = buffer->buffers[cpu];
3329 entries += rb_num_of_entries(cpu_buffer);
3332 return entries;
3334 EXPORT_SYMBOL_GPL(ring_buffer_entries);
3337 * ring_buffer_overruns - get the number of overruns in buffer
3338 * @buffer: The ring buffer
3340 * Returns the total number of overruns in the ring buffer
3341 * (all CPU entries)
3343 unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3345 struct ring_buffer_per_cpu *cpu_buffer;
3346 unsigned long overruns = 0;
3347 int cpu;
3349 /* if you care about this being correct, lock the buffer */
3350 for_each_buffer_cpu(buffer, cpu) {
3351 cpu_buffer = buffer->buffers[cpu];
3352 overruns += local_read(&cpu_buffer->overrun);
3355 return overruns;
3357 EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3359 static void rb_iter_reset(struct ring_buffer_iter *iter)
3361 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3363 /* Iterator usage is expected to have record disabled */
3364 iter->head_page = cpu_buffer->reader_page;
3365 iter->head = cpu_buffer->reader_page->read;
3367 iter->cache_reader_page = iter->head_page;
3368 iter->cache_read = cpu_buffer->read;
3370 if (iter->head)
3371 iter->read_stamp = cpu_buffer->read_stamp;
3372 else
3373 iter->read_stamp = iter->head_page->page->time_stamp;
3377 * ring_buffer_iter_reset - reset an iterator
3378 * @iter: The iterator to reset
3380 * Resets the iterator, so that it will start from the beginning
3381 * again.
3383 void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3385 struct ring_buffer_per_cpu *cpu_buffer;
3386 unsigned long flags;
3388 if (!iter)
3389 return;
3391 cpu_buffer = iter->cpu_buffer;
3393 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3394 rb_iter_reset(iter);
3395 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3397 EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3400 * ring_buffer_iter_empty - check if an iterator has no more to read
3401 * @iter: The iterator to check
3403 int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3405 struct ring_buffer_per_cpu *cpu_buffer;
3407 cpu_buffer = iter->cpu_buffer;
3409 return iter->head_page == cpu_buffer->commit_page &&
3410 iter->head == rb_commit_index(cpu_buffer);
3412 EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3414 static void
3415 rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3416 struct ring_buffer_event *event)
3418 u64 delta;
3420 switch (event->type_len) {
3421 case RINGBUF_TYPE_PADDING:
3422 return;
3424 case RINGBUF_TYPE_TIME_EXTEND:
3425 delta = event->array[0];
3426 delta <<= TS_SHIFT;
3427 delta += event->time_delta;
3428 cpu_buffer->read_stamp += delta;
3429 return;
3431 case RINGBUF_TYPE_TIME_STAMP:
3432 /* FIXME: not implemented */
3433 return;
3435 case RINGBUF_TYPE_DATA:
3436 cpu_buffer->read_stamp += event->time_delta;
3437 return;
3439 default:
3440 BUG();
3442 return;
3445 static void
3446 rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3447 struct ring_buffer_event *event)
3449 u64 delta;
3451 switch (event->type_len) {
3452 case RINGBUF_TYPE_PADDING:
3453 return;
3455 case RINGBUF_TYPE_TIME_EXTEND:
3456 delta = event->array[0];
3457 delta <<= TS_SHIFT;
3458 delta += event->time_delta;
3459 iter->read_stamp += delta;
3460 return;
3462 case RINGBUF_TYPE_TIME_STAMP:
3463 /* FIXME: not implemented */
3464 return;
3466 case RINGBUF_TYPE_DATA:
3467 iter->read_stamp += event->time_delta;
3468 return;
3470 default:
3471 BUG();
3473 return;
3476 static struct buffer_page *
3477 rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3479 struct buffer_page *reader = NULL;
3480 unsigned long overwrite;
3481 unsigned long flags;
3482 int nr_loops = 0;
3483 int ret;
3485 local_irq_save(flags);
3486 arch_spin_lock(&cpu_buffer->lock);
3488 again:
3490 * This should normally only loop twice. But because the
3491 * start of the reader inserts an empty page, it causes
3492 * a case where we will loop three times. There should be no
3493 * reason to loop four times (that I know of).
3495 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3496 reader = NULL;
3497 goto out;
3500 reader = cpu_buffer->reader_page;
3502 /* If there's more to read, return this page */
3503 if (cpu_buffer->reader_page->read < rb_page_size(reader))
3504 goto out;
3506 /* Never should we have an index greater than the size */
3507 if (RB_WARN_ON(cpu_buffer,
3508 cpu_buffer->reader_page->read > rb_page_size(reader)))
3509 goto out;
3511 /* check if we caught up to the tail */
3512 reader = NULL;
3513 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3514 goto out;
3516 /* Don't bother swapping if the ring buffer is empty */
3517 if (rb_num_of_entries(cpu_buffer) == 0)
3518 goto out;
3521 * Reset the reader page to size zero.
3523 local_set(&cpu_buffer->reader_page->write, 0);
3524 local_set(&cpu_buffer->reader_page->entries, 0);
3525 local_set(&cpu_buffer->reader_page->page->commit, 0);
3526 cpu_buffer->reader_page->real_end = 0;
3528 spin:
3530 * Splice the empty reader page into the list around the head.
3532 reader = rb_set_head_page(cpu_buffer);
3533 if (!reader)
3534 goto out;
3535 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3536 cpu_buffer->reader_page->list.prev = reader->list.prev;
3539 * cpu_buffer->pages just needs to point to the buffer, it
3540 * has no specific buffer page to point to. Lets move it out
3541 * of our way so we don't accidentally swap it.
3543 cpu_buffer->pages = reader->list.prev;
3545 /* The reader page will be pointing to the new head */
3546 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3549 * We want to make sure we read the overruns after we set up our
3550 * pointers to the next object. The writer side does a
3551 * cmpxchg to cross pages which acts as the mb on the writer
3552 * side. Note, the reader will constantly fail the swap
3553 * while the writer is updating the pointers, so this
3554 * guarantees that the overwrite recorded here is the one we
3555 * want to compare with the last_overrun.
3557 smp_mb();
3558 overwrite = local_read(&(cpu_buffer->overrun));
3561 * Here's the tricky part.
3563 * We need to move the pointer past the header page.
3564 * But we can only do that if a writer is not currently
3565 * moving it. The page before the header page has the
3566 * flag bit '1' set if it is pointing to the page we want.
3567 * but if the writer is in the process of moving it
3568 * than it will be '2' or already moved '0'.
3571 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3574 * If we did not convert it, then we must try again.
3576 if (!ret)
3577 goto spin;
3580 * Yeah! We succeeded in replacing the page.
3582 * Now make the new head point back to the reader page.
3584 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3585 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3587 /* Finally update the reader page to the new head */
3588 cpu_buffer->reader_page = reader;
3589 rb_reset_reader_page(cpu_buffer);
3591 if (overwrite != cpu_buffer->last_overrun) {
3592 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3593 cpu_buffer->last_overrun = overwrite;
3596 goto again;
3598 out:
3599 arch_spin_unlock(&cpu_buffer->lock);
3600 local_irq_restore(flags);
3602 return reader;
3605 static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3607 struct ring_buffer_event *event;
3608 struct buffer_page *reader;
3609 unsigned length;
3611 reader = rb_get_reader_page(cpu_buffer);
3613 /* This function should not be called when buffer is empty */
3614 if (RB_WARN_ON(cpu_buffer, !reader))
3615 return;
3617 event = rb_reader_event(cpu_buffer);
3619 if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3620 cpu_buffer->read++;
3622 rb_update_read_stamp(cpu_buffer, event);
3624 length = rb_event_length(event);
3625 cpu_buffer->reader_page->read += length;
3628 static void rb_advance_iter(struct ring_buffer_iter *iter)
3630 struct ring_buffer_per_cpu *cpu_buffer;
3631 struct ring_buffer_event *event;
3632 unsigned length;
3634 cpu_buffer = iter->cpu_buffer;
3637 * Check if we are at the end of the buffer.
3639 if (iter->head >= rb_page_size(iter->head_page)) {
3640 /* discarded commits can make the page empty */
3641 if (iter->head_page == cpu_buffer->commit_page)
3642 return;
3643 rb_inc_iter(iter);
3644 return;
3647 event = rb_iter_head_event(iter);
3649 length = rb_event_length(event);
3652 * This should not be called to advance the header if we are
3653 * at the tail of the buffer.
3655 if (RB_WARN_ON(cpu_buffer,
3656 (iter->head_page == cpu_buffer->commit_page) &&
3657 (iter->head + length > rb_commit_index(cpu_buffer))))
3658 return;
3660 rb_update_iter_read_stamp(iter, event);
3662 iter->head += length;
3664 /* check for end of page padding */
3665 if ((iter->head >= rb_page_size(iter->head_page)) &&
3666 (iter->head_page != cpu_buffer->commit_page))
3667 rb_inc_iter(iter);
3670 static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3672 return cpu_buffer->lost_events;
3675 static struct ring_buffer_event *
3676 rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3677 unsigned long *lost_events)
3679 struct ring_buffer_event *event;
3680 struct buffer_page *reader;
3681 int nr_loops = 0;
3683 again:
3685 * We repeat when a time extend is encountered.
3686 * Since the time extend is always attached to a data event,
3687 * we should never loop more than once.
3688 * (We never hit the following condition more than twice).
3690 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3691 return NULL;
3693 reader = rb_get_reader_page(cpu_buffer);
3694 if (!reader)
3695 return NULL;
3697 event = rb_reader_event(cpu_buffer);
3699 switch (event->type_len) {
3700 case RINGBUF_TYPE_PADDING:
3701 if (rb_null_event(event))
3702 RB_WARN_ON(cpu_buffer, 1);
3704 * Because the writer could be discarding every
3705 * event it creates (which would probably be bad)
3706 * if we were to go back to "again" then we may never
3707 * catch up, and will trigger the warn on, or lock
3708 * the box. Return the padding, and we will release
3709 * the current locks, and try again.
3711 return event;
3713 case RINGBUF_TYPE_TIME_EXTEND:
3714 /* Internal data, OK to advance */
3715 rb_advance_reader(cpu_buffer);
3716 goto again;
3718 case RINGBUF_TYPE_TIME_STAMP:
3719 /* FIXME: not implemented */
3720 rb_advance_reader(cpu_buffer);
3721 goto again;
3723 case RINGBUF_TYPE_DATA:
3724 if (ts) {
3725 *ts = cpu_buffer->read_stamp + event->time_delta;
3726 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3727 cpu_buffer->cpu, ts);
3729 if (lost_events)
3730 *lost_events = rb_lost_events(cpu_buffer);
3731 return event;
3733 default:
3734 BUG();
3737 return NULL;
3739 EXPORT_SYMBOL_GPL(ring_buffer_peek);
3741 static struct ring_buffer_event *
3742 rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3744 struct ring_buffer *buffer;
3745 struct ring_buffer_per_cpu *cpu_buffer;
3746 struct ring_buffer_event *event;
3747 int nr_loops = 0;
3749 cpu_buffer = iter->cpu_buffer;
3750 buffer = cpu_buffer->buffer;
3753 * Check if someone performed a consuming read to
3754 * the buffer. A consuming read invalidates the iterator
3755 * and we need to reset the iterator in this case.
3757 if (unlikely(iter->cache_read != cpu_buffer->read ||
3758 iter->cache_reader_page != cpu_buffer->reader_page))
3759 rb_iter_reset(iter);
3761 again:
3762 if (ring_buffer_iter_empty(iter))
3763 return NULL;
3766 * We repeat when a time extend is encountered or we hit
3767 * the end of the page. Since the time extend is always attached
3768 * to a data event, we should never loop more than three times.
3769 * Once for going to next page, once on time extend, and
3770 * finally once to get the event.
3771 * (We never hit the following condition more than thrice).
3773 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3))
3774 return NULL;
3776 if (rb_per_cpu_empty(cpu_buffer))
3777 return NULL;
3779 if (iter->head >= rb_page_size(iter->head_page)) {
3780 rb_inc_iter(iter);
3781 goto again;
3784 event = rb_iter_head_event(iter);
3786 switch (event->type_len) {
3787 case RINGBUF_TYPE_PADDING:
3788 if (rb_null_event(event)) {
3789 rb_inc_iter(iter);
3790 goto again;
3792 rb_advance_iter(iter);
3793 return event;
3795 case RINGBUF_TYPE_TIME_EXTEND:
3796 /* Internal data, OK to advance */
3797 rb_advance_iter(iter);
3798 goto again;
3800 case RINGBUF_TYPE_TIME_STAMP:
3801 /* FIXME: not implemented */
3802 rb_advance_iter(iter);
3803 goto again;
3805 case RINGBUF_TYPE_DATA:
3806 if (ts) {
3807 *ts = iter->read_stamp + event->time_delta;
3808 ring_buffer_normalize_time_stamp(buffer,
3809 cpu_buffer->cpu, ts);
3811 return event;
3813 default:
3814 BUG();
3817 return NULL;
3819 EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
3821 static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
3823 if (likely(!in_nmi())) {
3824 raw_spin_lock(&cpu_buffer->reader_lock);
3825 return true;
3829 * If an NMI die dumps out the content of the ring buffer
3830 * trylock must be used to prevent a deadlock if the NMI
3831 * preempted a task that holds the ring buffer locks. If
3832 * we get the lock then all is fine, if not, then continue
3833 * to do the read, but this can corrupt the ring buffer,
3834 * so it must be permanently disabled from future writes.
3835 * Reading from NMI is a oneshot deal.
3837 if (raw_spin_trylock(&cpu_buffer->reader_lock))
3838 return true;
3840 /* Continue without locking, but disable the ring buffer */
3841 atomic_inc(&cpu_buffer->record_disabled);
3842 return false;
3845 static inline void
3846 rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
3848 if (likely(locked))
3849 raw_spin_unlock(&cpu_buffer->reader_lock);
3850 return;
3854 * ring_buffer_peek - peek at the next event to be read
3855 * @buffer: The ring buffer to read
3856 * @cpu: The cpu to peak at
3857 * @ts: The timestamp counter of this event.
3858 * @lost_events: a variable to store if events were lost (may be NULL)
3860 * This will return the event that will be read next, but does
3861 * not consume the data.
3863 struct ring_buffer_event *
3864 ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
3865 unsigned long *lost_events)
3867 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3868 struct ring_buffer_event *event;
3869 unsigned long flags;
3870 bool dolock;
3872 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3873 return NULL;
3875 again:
3876 local_irq_save(flags);
3877 dolock = rb_reader_lock(cpu_buffer);
3878 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3879 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3880 rb_advance_reader(cpu_buffer);
3881 rb_reader_unlock(cpu_buffer, dolock);
3882 local_irq_restore(flags);
3884 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3885 goto again;
3887 return event;
3891 * ring_buffer_iter_peek - peek at the next event to be read
3892 * @iter: The ring buffer iterator
3893 * @ts: The timestamp counter of this event.
3895 * This will return the event that will be read next, but does
3896 * not increment the iterator.
3898 struct ring_buffer_event *
3899 ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3901 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3902 struct ring_buffer_event *event;
3903 unsigned long flags;
3905 again:
3906 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3907 event = rb_iter_peek(iter, ts);
3908 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3910 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3911 goto again;
3913 return event;
3917 * ring_buffer_consume - return an event and consume it
3918 * @buffer: The ring buffer to get the next event from
3919 * @cpu: the cpu to read the buffer from
3920 * @ts: a variable to store the timestamp (may be NULL)
3921 * @lost_events: a variable to store if events were lost (may be NULL)
3923 * Returns the next event in the ring buffer, and that event is consumed.
3924 * Meaning, that sequential reads will keep returning a different event,
3925 * and eventually empty the ring buffer if the producer is slower.
3927 struct ring_buffer_event *
3928 ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
3929 unsigned long *lost_events)
3931 struct ring_buffer_per_cpu *cpu_buffer;
3932 struct ring_buffer_event *event = NULL;
3933 unsigned long flags;
3934 bool dolock;
3936 again:
3937 /* might be called in atomic */
3938 preempt_disable();
3940 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3941 goto out;
3943 cpu_buffer = buffer->buffers[cpu];
3944 local_irq_save(flags);
3945 dolock = rb_reader_lock(cpu_buffer);
3947 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3948 if (event) {
3949 cpu_buffer->lost_events = 0;
3950 rb_advance_reader(cpu_buffer);
3953 rb_reader_unlock(cpu_buffer, dolock);
3954 local_irq_restore(flags);
3956 out:
3957 preempt_enable();
3959 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3960 goto again;
3962 return event;
3964 EXPORT_SYMBOL_GPL(ring_buffer_consume);
3967 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
3968 * @buffer: The ring buffer to read from
3969 * @cpu: The cpu buffer to iterate over
3971 * This performs the initial preparations necessary to iterate
3972 * through the buffer. Memory is allocated, buffer recording
3973 * is disabled, and the iterator pointer is returned to the caller.
3975 * Disabling buffer recordng prevents the reading from being
3976 * corrupted. This is not a consuming read, so a producer is not
3977 * expected.
3979 * After a sequence of ring_buffer_read_prepare calls, the user is
3980 * expected to make at least one call to ring_buffer_read_prepare_sync.
3981 * Afterwards, ring_buffer_read_start is invoked to get things going
3982 * for real.
3984 * This overall must be paired with ring_buffer_read_finish.
3986 struct ring_buffer_iter *
3987 ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
3989 struct ring_buffer_per_cpu *cpu_buffer;
3990 struct ring_buffer_iter *iter;
3992 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3993 return NULL;
3995 iter = kmalloc(sizeof(*iter), GFP_KERNEL);
3996 if (!iter)
3997 return NULL;
3999 cpu_buffer = buffer->buffers[cpu];
4001 iter->cpu_buffer = cpu_buffer;
4003 atomic_inc(&buffer->resize_disabled);
4004 atomic_inc(&cpu_buffer->record_disabled);
4006 return iter;
4008 EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
4011 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
4013 * All previously invoked ring_buffer_read_prepare calls to prepare
4014 * iterators will be synchronized. Afterwards, read_buffer_read_start
4015 * calls on those iterators are allowed.
4017 void
4018 ring_buffer_read_prepare_sync(void)
4020 synchronize_sched();
4022 EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
4025 * ring_buffer_read_start - start a non consuming read of the buffer
4026 * @iter: The iterator returned by ring_buffer_read_prepare
4028 * This finalizes the startup of an iteration through the buffer.
4029 * The iterator comes from a call to ring_buffer_read_prepare and
4030 * an intervening ring_buffer_read_prepare_sync must have been
4031 * performed.
4033 * Must be paired with ring_buffer_read_finish.
4035 void
4036 ring_buffer_read_start(struct ring_buffer_iter *iter)
4038 struct ring_buffer_per_cpu *cpu_buffer;
4039 unsigned long flags;
4041 if (!iter)
4042 return;
4044 cpu_buffer = iter->cpu_buffer;
4046 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4047 arch_spin_lock(&cpu_buffer->lock);
4048 rb_iter_reset(iter);
4049 arch_spin_unlock(&cpu_buffer->lock);
4050 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4052 EXPORT_SYMBOL_GPL(ring_buffer_read_start);
4055 * ring_buffer_read_finish - finish reading the iterator of the buffer
4056 * @iter: The iterator retrieved by ring_buffer_start
4058 * This re-enables the recording to the buffer, and frees the
4059 * iterator.
4061 void
4062 ring_buffer_read_finish(struct ring_buffer_iter *iter)
4064 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4065 unsigned long flags;
4068 * Ring buffer is disabled from recording, here's a good place
4069 * to check the integrity of the ring buffer.
4070 * Must prevent readers from trying to read, as the check
4071 * clears the HEAD page and readers require it.
4073 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4074 rb_check_pages(cpu_buffer);
4075 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4077 atomic_dec(&cpu_buffer->record_disabled);
4078 atomic_dec(&cpu_buffer->buffer->resize_disabled);
4079 kfree(iter);
4081 EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
4084 * ring_buffer_read - read the next item in the ring buffer by the iterator
4085 * @iter: The ring buffer iterator
4086 * @ts: The time stamp of the event read.
4088 * This reads the next event in the ring buffer and increments the iterator.
4090 struct ring_buffer_event *
4091 ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
4093 struct ring_buffer_event *event;
4094 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4095 unsigned long flags;
4097 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4098 again:
4099 event = rb_iter_peek(iter, ts);
4100 if (!event)
4101 goto out;
4103 if (event->type_len == RINGBUF_TYPE_PADDING)
4104 goto again;
4106 rb_advance_iter(iter);
4107 out:
4108 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4110 return event;
4112 EXPORT_SYMBOL_GPL(ring_buffer_read);
4115 * ring_buffer_size - return the size of the ring buffer (in bytes)
4116 * @buffer: The ring buffer.
4118 unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
4121 * Earlier, this method returned
4122 * BUF_PAGE_SIZE * buffer->nr_pages
4123 * Since the nr_pages field is now removed, we have converted this to
4124 * return the per cpu buffer value.
4126 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4127 return 0;
4129 return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
4131 EXPORT_SYMBOL_GPL(ring_buffer_size);
4133 static void
4134 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
4136 rb_head_page_deactivate(cpu_buffer);
4138 cpu_buffer->head_page
4139 = list_entry(cpu_buffer->pages, struct buffer_page, list);
4140 local_set(&cpu_buffer->head_page->write, 0);
4141 local_set(&cpu_buffer->head_page->entries, 0);
4142 local_set(&cpu_buffer->head_page->page->commit, 0);
4144 cpu_buffer->head_page->read = 0;
4146 cpu_buffer->tail_page = cpu_buffer->head_page;
4147 cpu_buffer->commit_page = cpu_buffer->head_page;
4149 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
4150 INIT_LIST_HEAD(&cpu_buffer->new_pages);
4151 local_set(&cpu_buffer->reader_page->write, 0);
4152 local_set(&cpu_buffer->reader_page->entries, 0);
4153 local_set(&cpu_buffer->reader_page->page->commit, 0);
4154 cpu_buffer->reader_page->read = 0;
4156 local_set(&cpu_buffer->entries_bytes, 0);
4157 local_set(&cpu_buffer->overrun, 0);
4158 local_set(&cpu_buffer->commit_overrun, 0);
4159 local_set(&cpu_buffer->dropped_events, 0);
4160 local_set(&cpu_buffer->entries, 0);
4161 local_set(&cpu_buffer->committing, 0);
4162 local_set(&cpu_buffer->commits, 0);
4163 cpu_buffer->read = 0;
4164 cpu_buffer->read_bytes = 0;
4166 cpu_buffer->write_stamp = 0;
4167 cpu_buffer->read_stamp = 0;
4169 cpu_buffer->lost_events = 0;
4170 cpu_buffer->last_overrun = 0;
4172 rb_head_page_activate(cpu_buffer);
4176 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
4177 * @buffer: The ring buffer to reset a per cpu buffer of
4178 * @cpu: The CPU buffer to be reset
4180 void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
4182 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4183 unsigned long flags;
4185 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4186 return;
4188 atomic_inc(&buffer->resize_disabled);
4189 atomic_inc(&cpu_buffer->record_disabled);
4191 /* Make sure all commits have finished */
4192 synchronize_sched();
4194 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4196 if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
4197 goto out;
4199 arch_spin_lock(&cpu_buffer->lock);
4201 rb_reset_cpu(cpu_buffer);
4203 arch_spin_unlock(&cpu_buffer->lock);
4205 out:
4206 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4208 atomic_dec(&cpu_buffer->record_disabled);
4209 atomic_dec(&buffer->resize_disabled);
4211 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
4214 * ring_buffer_reset - reset a ring buffer
4215 * @buffer: The ring buffer to reset all cpu buffers
4217 void ring_buffer_reset(struct ring_buffer *buffer)
4219 int cpu;
4221 for_each_buffer_cpu(buffer, cpu)
4222 ring_buffer_reset_cpu(buffer, cpu);
4224 EXPORT_SYMBOL_GPL(ring_buffer_reset);
4227 * rind_buffer_empty - is the ring buffer empty?
4228 * @buffer: The ring buffer to test
4230 int ring_buffer_empty(struct ring_buffer *buffer)
4232 struct ring_buffer_per_cpu *cpu_buffer;
4233 unsigned long flags;
4234 bool dolock;
4235 int cpu;
4236 int ret;
4238 /* yes this is racy, but if you don't like the race, lock the buffer */
4239 for_each_buffer_cpu(buffer, cpu) {
4240 cpu_buffer = buffer->buffers[cpu];
4241 local_irq_save(flags);
4242 dolock = rb_reader_lock(cpu_buffer);
4243 ret = rb_per_cpu_empty(cpu_buffer);
4244 rb_reader_unlock(cpu_buffer, dolock);
4245 local_irq_restore(flags);
4247 if (!ret)
4248 return 0;
4251 return 1;
4253 EXPORT_SYMBOL_GPL(ring_buffer_empty);
4256 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
4257 * @buffer: The ring buffer
4258 * @cpu: The CPU buffer to test
4260 int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
4262 struct ring_buffer_per_cpu *cpu_buffer;
4263 unsigned long flags;
4264 bool dolock;
4265 int ret;
4267 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4268 return 1;
4270 cpu_buffer = buffer->buffers[cpu];
4271 local_irq_save(flags);
4272 dolock = rb_reader_lock(cpu_buffer);
4273 ret = rb_per_cpu_empty(cpu_buffer);
4274 rb_reader_unlock(cpu_buffer, dolock);
4275 local_irq_restore(flags);
4277 return ret;
4279 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
4281 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
4283 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
4284 * @buffer_a: One buffer to swap with
4285 * @buffer_b: The other buffer to swap with
4287 * This function is useful for tracers that want to take a "snapshot"
4288 * of a CPU buffer and has another back up buffer lying around.
4289 * it is expected that the tracer handles the cpu buffer not being
4290 * used at the moment.
4292 int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
4293 struct ring_buffer *buffer_b, int cpu)
4295 struct ring_buffer_per_cpu *cpu_buffer_a;
4296 struct ring_buffer_per_cpu *cpu_buffer_b;
4297 int ret = -EINVAL;
4299 if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
4300 !cpumask_test_cpu(cpu, buffer_b->cpumask))
4301 goto out;
4303 cpu_buffer_a = buffer_a->buffers[cpu];
4304 cpu_buffer_b = buffer_b->buffers[cpu];
4306 /* At least make sure the two buffers are somewhat the same */
4307 if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
4308 goto out;
4310 ret = -EAGAIN;
4312 if (atomic_read(&buffer_a->record_disabled))
4313 goto out;
4315 if (atomic_read(&buffer_b->record_disabled))
4316 goto out;
4318 if (atomic_read(&cpu_buffer_a->record_disabled))
4319 goto out;
4321 if (atomic_read(&cpu_buffer_b->record_disabled))
4322 goto out;
4325 * We can't do a synchronize_sched here because this
4326 * function can be called in atomic context.
4327 * Normally this will be called from the same CPU as cpu.
4328 * If not it's up to the caller to protect this.
4330 atomic_inc(&cpu_buffer_a->record_disabled);
4331 atomic_inc(&cpu_buffer_b->record_disabled);
4333 ret = -EBUSY;
4334 if (local_read(&cpu_buffer_a->committing))
4335 goto out_dec;
4336 if (local_read(&cpu_buffer_b->committing))
4337 goto out_dec;
4339 buffer_a->buffers[cpu] = cpu_buffer_b;
4340 buffer_b->buffers[cpu] = cpu_buffer_a;
4342 cpu_buffer_b->buffer = buffer_a;
4343 cpu_buffer_a->buffer = buffer_b;
4345 ret = 0;
4347 out_dec:
4348 atomic_dec(&cpu_buffer_a->record_disabled);
4349 atomic_dec(&cpu_buffer_b->record_disabled);
4350 out:
4351 return ret;
4353 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
4354 #endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
4357 * ring_buffer_alloc_read_page - allocate a page to read from buffer
4358 * @buffer: the buffer to allocate for.
4359 * @cpu: the cpu buffer to allocate.
4361 * This function is used in conjunction with ring_buffer_read_page.
4362 * When reading a full page from the ring buffer, these functions
4363 * can be used to speed up the process. The calling function should
4364 * allocate a few pages first with this function. Then when it
4365 * needs to get pages from the ring buffer, it passes the result
4366 * of this function into ring_buffer_read_page, which will swap
4367 * the page that was allocated, with the read page of the buffer.
4369 * Returns:
4370 * The page allocated, or NULL on error.
4372 void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
4374 struct buffer_data_page *bpage;
4375 struct page *page;
4377 page = alloc_pages_node(cpu_to_node(cpu),
4378 GFP_KERNEL | __GFP_NORETRY, 0);
4379 if (!page)
4380 return NULL;
4382 bpage = page_address(page);
4384 rb_init_page(bpage);
4386 return bpage;
4388 EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
4391 * ring_buffer_free_read_page - free an allocated read page
4392 * @buffer: the buffer the page was allocate for
4393 * @data: the page to free
4395 * Free a page allocated from ring_buffer_alloc_read_page.
4397 void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
4399 free_page((unsigned long)data);
4401 EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
4404 * ring_buffer_read_page - extract a page from the ring buffer
4405 * @buffer: buffer to extract from
4406 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
4407 * @len: amount to extract
4408 * @cpu: the cpu of the buffer to extract
4409 * @full: should the extraction only happen when the page is full.
4411 * This function will pull out a page from the ring buffer and consume it.
4412 * @data_page must be the address of the variable that was returned
4413 * from ring_buffer_alloc_read_page. This is because the page might be used
4414 * to swap with a page in the ring buffer.
4416 * for example:
4417 * rpage = ring_buffer_alloc_read_page(buffer, cpu);
4418 * if (!rpage)
4419 * return error;
4420 * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
4421 * if (ret >= 0)
4422 * process_page(rpage, ret);
4424 * When @full is set, the function will not return true unless
4425 * the writer is off the reader page.
4427 * Note: it is up to the calling functions to handle sleeps and wakeups.
4428 * The ring buffer can be used anywhere in the kernel and can not
4429 * blindly call wake_up. The layer that uses the ring buffer must be
4430 * responsible for that.
4432 * Returns:
4433 * >=0 if data has been transferred, returns the offset of consumed data.
4434 * <0 if no data has been transferred.
4436 int ring_buffer_read_page(struct ring_buffer *buffer,
4437 void **data_page, size_t len, int cpu, int full)
4439 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4440 struct ring_buffer_event *event;
4441 struct buffer_data_page *bpage;
4442 struct buffer_page *reader;
4443 unsigned long missed_events;
4444 unsigned long flags;
4445 unsigned int commit;
4446 unsigned int read;
4447 u64 save_timestamp;
4448 int ret = -1;
4450 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4451 goto out;
4454 * If len is not big enough to hold the page header, then
4455 * we can not copy anything.
4457 if (len <= BUF_PAGE_HDR_SIZE)
4458 goto out;
4460 len -= BUF_PAGE_HDR_SIZE;
4462 if (!data_page)
4463 goto out;
4465 bpage = *data_page;
4466 if (!bpage)
4467 goto out;
4469 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4471 reader = rb_get_reader_page(cpu_buffer);
4472 if (!reader)
4473 goto out_unlock;
4475 event = rb_reader_event(cpu_buffer);
4477 read = reader->read;
4478 commit = rb_page_commit(reader);
4480 /* Check if any events were dropped */
4481 missed_events = cpu_buffer->lost_events;
4484 * If this page has been partially read or
4485 * if len is not big enough to read the rest of the page or
4486 * a writer is still on the page, then
4487 * we must copy the data from the page to the buffer.
4488 * Otherwise, we can simply swap the page with the one passed in.
4490 if (read || (len < (commit - read)) ||
4491 cpu_buffer->reader_page == cpu_buffer->commit_page) {
4492 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
4493 unsigned int rpos = read;
4494 unsigned int pos = 0;
4495 unsigned int size;
4497 if (full)
4498 goto out_unlock;
4500 if (len > (commit - read))
4501 len = (commit - read);
4503 /* Always keep the time extend and data together */
4504 size = rb_event_ts_length(event);
4506 if (len < size)
4507 goto out_unlock;
4509 /* save the current timestamp, since the user will need it */
4510 save_timestamp = cpu_buffer->read_stamp;
4512 /* Need to copy one event at a time */
4513 do {
4514 /* We need the size of one event, because
4515 * rb_advance_reader only advances by one event,
4516 * whereas rb_event_ts_length may include the size of
4517 * one or two events.
4518 * We have already ensured there's enough space if this
4519 * is a time extend. */
4520 size = rb_event_length(event);
4521 memcpy(bpage->data + pos, rpage->data + rpos, size);
4523 len -= size;
4525 rb_advance_reader(cpu_buffer);
4526 rpos = reader->read;
4527 pos += size;
4529 if (rpos >= commit)
4530 break;
4532 event = rb_reader_event(cpu_buffer);
4533 /* Always keep the time extend and data together */
4534 size = rb_event_ts_length(event);
4535 } while (len >= size);
4537 /* update bpage */
4538 local_set(&bpage->commit, pos);
4539 bpage->time_stamp = save_timestamp;
4541 /* we copied everything to the beginning */
4542 read = 0;
4543 } else {
4544 /* update the entry counter */
4545 cpu_buffer->read += rb_page_entries(reader);
4546 cpu_buffer->read_bytes += BUF_PAGE_SIZE;
4548 /* swap the pages */
4549 rb_init_page(bpage);
4550 bpage = reader->page;
4551 reader->page = *data_page;
4552 local_set(&reader->write, 0);
4553 local_set(&reader->entries, 0);
4554 reader->read = 0;
4555 *data_page = bpage;
4558 * Use the real_end for the data size,
4559 * This gives us a chance to store the lost events
4560 * on the page.
4562 if (reader->real_end)
4563 local_set(&bpage->commit, reader->real_end);
4565 ret = read;
4567 cpu_buffer->lost_events = 0;
4569 commit = local_read(&bpage->commit);
4571 * Set a flag in the commit field if we lost events
4573 if (missed_events) {
4574 /* If there is room at the end of the page to save the
4575 * missed events, then record it there.
4577 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
4578 memcpy(&bpage->data[commit], &missed_events,
4579 sizeof(missed_events));
4580 local_add(RB_MISSED_STORED, &bpage->commit);
4581 commit += sizeof(missed_events);
4583 local_add(RB_MISSED_EVENTS, &bpage->commit);
4587 * This page may be off to user land. Zero it out here.
4589 if (commit < BUF_PAGE_SIZE)
4590 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
4592 out_unlock:
4593 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4595 out:
4596 return ret;
4598 EXPORT_SYMBOL_GPL(ring_buffer_read_page);
4600 #ifdef CONFIG_HOTPLUG_CPU
4601 static int rb_cpu_notify(struct notifier_block *self,
4602 unsigned long action, void *hcpu)
4604 struct ring_buffer *buffer =
4605 container_of(self, struct ring_buffer, cpu_notify);
4606 long cpu = (long)hcpu;
4607 int cpu_i, nr_pages_same;
4608 unsigned int nr_pages;
4610 switch (action) {
4611 case CPU_UP_PREPARE:
4612 case CPU_UP_PREPARE_FROZEN:
4613 if (cpumask_test_cpu(cpu, buffer->cpumask))
4614 return NOTIFY_OK;
4616 nr_pages = 0;
4617 nr_pages_same = 1;
4618 /* check if all cpu sizes are same */
4619 for_each_buffer_cpu(buffer, cpu_i) {
4620 /* fill in the size from first enabled cpu */
4621 if (nr_pages == 0)
4622 nr_pages = buffer->buffers[cpu_i]->nr_pages;
4623 if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
4624 nr_pages_same = 0;
4625 break;
4628 /* allocate minimum pages, user can later expand it */
4629 if (!nr_pages_same)
4630 nr_pages = 2;
4631 buffer->buffers[cpu] =
4632 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
4633 if (!buffer->buffers[cpu]) {
4634 WARN(1, "failed to allocate ring buffer on CPU %ld\n",
4635 cpu);
4636 return NOTIFY_OK;
4638 smp_wmb();
4639 cpumask_set_cpu(cpu, buffer->cpumask);
4640 break;
4641 case CPU_DOWN_PREPARE:
4642 case CPU_DOWN_PREPARE_FROZEN:
4644 * Do nothing.
4645 * If we were to free the buffer, then the user would
4646 * lose any trace that was in the buffer.
4648 break;
4649 default:
4650 break;
4652 return NOTIFY_OK;
4654 #endif
4656 #ifdef CONFIG_RING_BUFFER_STARTUP_TEST
4658 * This is a basic integrity check of the ring buffer.
4659 * Late in the boot cycle this test will run when configured in.
4660 * It will kick off a thread per CPU that will go into a loop
4661 * writing to the per cpu ring buffer various sizes of data.
4662 * Some of the data will be large items, some small.
4664 * Another thread is created that goes into a spin, sending out
4665 * IPIs to the other CPUs to also write into the ring buffer.
4666 * this is to test the nesting ability of the buffer.
4668 * Basic stats are recorded and reported. If something in the
4669 * ring buffer should happen that's not expected, a big warning
4670 * is displayed and all ring buffers are disabled.
4672 static struct task_struct *rb_threads[NR_CPUS] __initdata;
4674 struct rb_test_data {
4675 struct ring_buffer *buffer;
4676 unsigned long events;
4677 unsigned long bytes_written;
4678 unsigned long bytes_alloc;
4679 unsigned long bytes_dropped;
4680 unsigned long events_nested;
4681 unsigned long bytes_written_nested;
4682 unsigned long bytes_alloc_nested;
4683 unsigned long bytes_dropped_nested;
4684 int min_size_nested;
4685 int max_size_nested;
4686 int max_size;
4687 int min_size;
4688 int cpu;
4689 int cnt;
4692 static struct rb_test_data rb_data[NR_CPUS] __initdata;
4694 /* 1 meg per cpu */
4695 #define RB_TEST_BUFFER_SIZE 1048576
4697 static char rb_string[] __initdata =
4698 "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
4699 "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
4700 "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
4702 static bool rb_test_started __initdata;
4704 struct rb_item {
4705 int size;
4706 char str[];
4709 static __init int rb_write_something(struct rb_test_data *data, bool nested)
4711 struct ring_buffer_event *event;
4712 struct rb_item *item;
4713 bool started;
4714 int event_len;
4715 int size;
4716 int len;
4717 int cnt;
4719 /* Have nested writes different that what is written */
4720 cnt = data->cnt + (nested ? 27 : 0);
4722 /* Multiply cnt by ~e, to make some unique increment */
4723 size = (data->cnt * 68 / 25) % (sizeof(rb_string) - 1);
4725 len = size + sizeof(struct rb_item);
4727 started = rb_test_started;
4728 /* read rb_test_started before checking buffer enabled */
4729 smp_rmb();
4731 event = ring_buffer_lock_reserve(data->buffer, len);
4732 if (!event) {
4733 /* Ignore dropped events before test starts. */
4734 if (started) {
4735 if (nested)
4736 data->bytes_dropped += len;
4737 else
4738 data->bytes_dropped_nested += len;
4740 return len;
4743 event_len = ring_buffer_event_length(event);
4745 if (RB_WARN_ON(data->buffer, event_len < len))
4746 goto out;
4748 item = ring_buffer_event_data(event);
4749 item->size = size;
4750 memcpy(item->str, rb_string, size);
4752 if (nested) {
4753 data->bytes_alloc_nested += event_len;
4754 data->bytes_written_nested += len;
4755 data->events_nested++;
4756 if (!data->min_size_nested || len < data->min_size_nested)
4757 data->min_size_nested = len;
4758 if (len > data->max_size_nested)
4759 data->max_size_nested = len;
4760 } else {
4761 data->bytes_alloc += event_len;
4762 data->bytes_written += len;
4763 data->events++;
4764 if (!data->min_size || len < data->min_size)
4765 data->max_size = len;
4766 if (len > data->max_size)
4767 data->max_size = len;
4770 out:
4771 ring_buffer_unlock_commit(data->buffer, event);
4773 return 0;
4776 static __init int rb_test(void *arg)
4778 struct rb_test_data *data = arg;
4780 while (!kthread_should_stop()) {
4781 rb_write_something(data, false);
4782 data->cnt++;
4784 set_current_state(TASK_INTERRUPTIBLE);
4785 /* Now sleep between a min of 100-300us and a max of 1ms */
4786 usleep_range(((data->cnt % 3) + 1) * 100, 1000);
4789 return 0;
4792 static __init void rb_ipi(void *ignore)
4794 struct rb_test_data *data;
4795 int cpu = smp_processor_id();
4797 data = &rb_data[cpu];
4798 rb_write_something(data, true);
4801 static __init int rb_hammer_test(void *arg)
4803 while (!kthread_should_stop()) {
4805 /* Send an IPI to all cpus to write data! */
4806 smp_call_function(rb_ipi, NULL, 1);
4807 /* No sleep, but for non preempt, let others run */
4808 schedule();
4811 return 0;
4814 static __init int test_ringbuffer(void)
4816 struct task_struct *rb_hammer;
4817 struct ring_buffer *buffer;
4818 int cpu;
4819 int ret = 0;
4821 pr_info("Running ring buffer tests...\n");
4823 buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
4824 if (WARN_ON(!buffer))
4825 return 0;
4827 /* Disable buffer so that threads can't write to it yet */
4828 ring_buffer_record_off(buffer);
4830 for_each_online_cpu(cpu) {
4831 rb_data[cpu].buffer = buffer;
4832 rb_data[cpu].cpu = cpu;
4833 rb_data[cpu].cnt = cpu;
4834 rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu],
4835 "rbtester/%d", cpu);
4836 if (WARN_ON(!rb_threads[cpu])) {
4837 pr_cont("FAILED\n");
4838 ret = -1;
4839 goto out_free;
4842 kthread_bind(rb_threads[cpu], cpu);
4843 wake_up_process(rb_threads[cpu]);
4846 /* Now create the rb hammer! */
4847 rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
4848 if (WARN_ON(!rb_hammer)) {
4849 pr_cont("FAILED\n");
4850 ret = -1;
4851 goto out_free;
4854 ring_buffer_record_on(buffer);
4856 * Show buffer is enabled before setting rb_test_started.
4857 * Yes there's a small race window where events could be
4858 * dropped and the thread wont catch it. But when a ring
4859 * buffer gets enabled, there will always be some kind of
4860 * delay before other CPUs see it. Thus, we don't care about
4861 * those dropped events. We care about events dropped after
4862 * the threads see that the buffer is active.
4864 smp_wmb();
4865 rb_test_started = true;
4867 set_current_state(TASK_INTERRUPTIBLE);
4868 /* Just run for 10 seconds */;
4869 schedule_timeout(10 * HZ);
4871 kthread_stop(rb_hammer);
4873 out_free:
4874 for_each_online_cpu(cpu) {
4875 if (!rb_threads[cpu])
4876 break;
4877 kthread_stop(rb_threads[cpu]);
4879 if (ret) {
4880 ring_buffer_free(buffer);
4881 return ret;
4884 /* Report! */
4885 pr_info("finished\n");
4886 for_each_online_cpu(cpu) {
4887 struct ring_buffer_event *event;
4888 struct rb_test_data *data = &rb_data[cpu];
4889 struct rb_item *item;
4890 unsigned long total_events;
4891 unsigned long total_dropped;
4892 unsigned long total_written;
4893 unsigned long total_alloc;
4894 unsigned long total_read = 0;
4895 unsigned long total_size = 0;
4896 unsigned long total_len = 0;
4897 unsigned long total_lost = 0;
4898 unsigned long lost;
4899 int big_event_size;
4900 int small_event_size;
4902 ret = -1;
4904 total_events = data->events + data->events_nested;
4905 total_written = data->bytes_written + data->bytes_written_nested;
4906 total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
4907 total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
4909 big_event_size = data->max_size + data->max_size_nested;
4910 small_event_size = data->min_size + data->min_size_nested;
4912 pr_info("CPU %d:\n", cpu);
4913 pr_info(" events: %ld\n", total_events);
4914 pr_info(" dropped bytes: %ld\n", total_dropped);
4915 pr_info(" alloced bytes: %ld\n", total_alloc);
4916 pr_info(" written bytes: %ld\n", total_written);
4917 pr_info(" biggest event: %d\n", big_event_size);
4918 pr_info(" smallest event: %d\n", small_event_size);
4920 if (RB_WARN_ON(buffer, total_dropped))
4921 break;
4923 ret = 0;
4925 while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
4926 total_lost += lost;
4927 item = ring_buffer_event_data(event);
4928 total_len += ring_buffer_event_length(event);
4929 total_size += item->size + sizeof(struct rb_item);
4930 if (memcmp(&item->str[0], rb_string, item->size) != 0) {
4931 pr_info("FAILED!\n");
4932 pr_info("buffer had: %.*s\n", item->size, item->str);
4933 pr_info("expected: %.*s\n", item->size, rb_string);
4934 RB_WARN_ON(buffer, 1);
4935 ret = -1;
4936 break;
4938 total_read++;
4940 if (ret)
4941 break;
4943 ret = -1;
4945 pr_info(" read events: %ld\n", total_read);
4946 pr_info(" lost events: %ld\n", total_lost);
4947 pr_info(" total events: %ld\n", total_lost + total_read);
4948 pr_info(" recorded len bytes: %ld\n", total_len);
4949 pr_info(" recorded size bytes: %ld\n", total_size);
4950 if (total_lost)
4951 pr_info(" With dropped events, record len and size may not match\n"
4952 " alloced and written from above\n");
4953 if (!total_lost) {
4954 if (RB_WARN_ON(buffer, total_len != total_alloc ||
4955 total_size != total_written))
4956 break;
4958 if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
4959 break;
4961 ret = 0;
4963 if (!ret)
4964 pr_info("Ring buffer PASSED!\n");
4966 ring_buffer_free(buffer);
4967 return 0;
4970 late_initcall(test_ringbuffer);
4971 #endif /* CONFIG_RING_BUFFER_STARTUP_TEST */