| Author | Tokens | Token Proportion | Commits | Commit Proportion |
|---|---|---|---|---|
| Steven Rostedt | 13291 | 81.99% | 133 | 62.74% |
| Vaibhav Nagarnaik | 1491 | 9.20% | 11 | 5.19% |
| Tom Zanussi | 505 | 3.12% | 4 | 1.89% |
| Robert Richter | 202 | 1.25% | 4 | 1.89% |
| Lai Jiangshan | 102 | 0.63% | 7 | 3.30% |
| Rabin Vincent | 92 | 0.57% | 1 | 0.47% |
| Slava Pestov | 86 | 0.53% | 1 | 0.47% |
| David Sharp | 64 | 0.39% | 3 | 1.42% |
| Sebastian Andrzej Siewior | 59 | 0.36% | 2 | 0.94% |
| David S. Miller | 53 | 0.33% | 1 | 0.47% |
| Rusty Russell | 46 | 0.28% | 2 | 0.94% |
| Peter Zijlstra | 30 | 0.19% | 1 | 0.47% |
| Thomas Gleixner | 25 | 0.15% | 4 | 1.89% |
| Masami Hiramatsu | 24 | 0.15% | 1 | 0.47% |
| Wei Yongjun | 17 | 0.10% | 1 | 0.47% |
| Ingo Molnar | 15 | 0.09% | 3 | 1.42% |
| Jovi Zhangwei | 11 | 0.07% | 2 | 0.94% |
| Vegard Nossum | 11 | 0.07% | 2 | 0.94% |
| Josef Bacik | 10 | 0.06% | 1 | 0.47% |
| Yaowei Bai | 10 | 0.06% | 4 | 1.89% |
| Linus Torvalds | 10 | 0.06% | 3 | 1.42% |
| James Hogan | 8 | 0.05% | 1 | 0.47% |
| Eric Dumazet | 7 | 0.04% | 1 | 0.47% |
| Huang Ying | 7 | 0.04% | 1 | 0.47% |
| Andrew Morton | 4 | 0.02% | 1 | 0.47% |
| Tejun Heo | 3 | 0.02% | 1 | 0.47% |
| Frédéric Weisbecker | 3 | 0.02% | 1 | 0.47% |
| Arnaldo Carvalho de Melo | 3 | 0.02% | 1 | 0.47% |
| Richard Kennedy | 3 | 0.02% | 1 | 0.47% |
| Wenji Huang | 2 | 0.01% | 1 | 0.47% |
| Wang Tianhong | 2 | 0.01% | 1 | 0.47% |
| Jiri Olsa | 2 | 0.01% | 2 | 0.94% |
| Corey Minyard | 2 | 0.01% | 1 | 0.47% |
| Adam Buchbinder | 2 | 0.01% | 1 | 0.47% |
| Yoshihiro Yunomae | 2 | 0.01% | 1 | 0.47% |
| Lucas De Marchi | 2 | 0.01% | 1 | 0.47% |
| Christoph Lameter | 1 | 0.01% | 1 | 0.47% |
| Chris Wilson | 1 | 0.01% | 1 | 0.47% |
| Jesper Juhl | 1 | 0.01% | 1 | 0.47% |
| Al Viro | 1 | 0.01% | 1 | 0.47% |
| Mark Rutland | 1 | 0.01% | 1 | 0.47% |
| Total | 16211 | 212 |
// SPDX-License-Identifier: GPL-2.0 /* * Generic ring buffer * * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com> */ #include <linux/trace_events.h> #include <linux/ring_buffer.h> #include <linux/trace_clock.h> #include <linux/sched/clock.h> #include <linux/trace_seq.h> #include <linux/spinlock.h> #include <linux/irq_work.h> #include <linux/uaccess.h> #include <linux/hardirq.h> #include <linux/kthread.h> /* for self test */ #include <linux/module.h> #include <linux/percpu.h> #include <linux/mutex.h> #include <linux/delay.h> #include <linux/slab.h> #include <linux/init.h> #include <linux/hash.h> #include <linux/list.h> #include <linux/cpu.h> #include <linux/oom.h> #include <asm/local.h> static void update_pages_handler(struct work_struct *work); /* * The ring buffer header is special. We must manually up keep it. */ int ring_buffer_print_entry_header(struct trace_seq *s) { trace_seq_puts(s, "# compressed entry header\n"); trace_seq_puts(s, "\ttype_len : 5 bits\n"); trace_seq_puts(s, "\ttime_delta : 27 bits\n"); trace_seq_puts(s, "\tarray : 32 bits\n"); trace_seq_putc(s, '\n'); trace_seq_printf(s, "\tpadding : type == %d\n", RINGBUF_TYPE_PADDING); trace_seq_printf(s, "\ttime_extend : type == %d\n", RINGBUF_TYPE_TIME_EXTEND); trace_seq_printf(s, "\ttime_stamp : type == %d\n", RINGBUF_TYPE_TIME_STAMP); trace_seq_printf(s, "\tdata max type_len == %d\n", RINGBUF_TYPE_DATA_TYPE_LEN_MAX); return !trace_seq_has_overflowed(s); } /* * The ring buffer is made up of a list of pages. A separate list of pages is * allocated for each CPU. A writer may only write to a buffer that is * associated with the CPU it is currently executing on. A reader may read * from any per cpu buffer. * * The reader is special. For each per cpu buffer, the reader has its own * reader page. When a reader has read the entire reader page, this reader * page is swapped with another page in the ring buffer. * * Now, as long as the writer is off the reader page, the reader can do what * ever it wants with that page. The writer will never write to that page * again (as long as it is out of the ring buffer). * * Here's some silly ASCII art. * * +------+ * |reader| RING BUFFER * |page | * +------+ +---+ +---+ +---+ * | |-->| |-->| | * +---+ +---+ +---+ * ^ | * | | * +---------------+ * * * +------+ * |reader| RING BUFFER * |page |------------------v * +------+ +---+ +---+ +---+ * | |-->| |-->| | * +---+ +---+ +---+ * ^ | * | | * +---------------+ * * * +------+ * |reader| RING BUFFER * |page |------------------v * +------+ +---+ +---+ +---+ * ^ | |-->| |-->| | * | +---+ +---+ +---+ * | | * | | * +------------------------------+ * * * +------+ * |buffer| RING BUFFER * |page |------------------v * +------+ +---+ +---+ +---+ * ^ | | | |-->| | * | New +---+ +---+ +---+ * | Reader------^ | * | page | * +------------------------------+ * * * After we make this swap, the reader can hand this page off to the splice * code and be done with it. It can even allocate a new page if it needs to * and swap that into the ring buffer. * * We will be using cmpxchg soon to make all this lockless. * */ /* Used for individual buffers (after the counter) */ #define RB_BUFFER_OFF (1 << 20) #define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data) #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array)) #define RB_ALIGNMENT 4U #define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX) #define RB_EVNT_MIN_SIZE 8U /* two 32bit words */ #ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS # define RB_FORCE_8BYTE_ALIGNMENT 0 # define RB_ARCH_ALIGNMENT RB_ALIGNMENT #else # define RB_FORCE_8BYTE_ALIGNMENT 1 # define RB_ARCH_ALIGNMENT 8U #endif #define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT) /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */ #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX enum { RB_LEN_TIME_EXTEND = 8, RB_LEN_TIME_STAMP = 8, }; #define skip_time_extend(event) \ ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND)) #define extended_time(event) \ (event->type_len >= RINGBUF_TYPE_TIME_EXTEND) static inline int rb_null_event(struct ring_buffer_event *event) { return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta; } static void rb_event_set_padding(struct ring_buffer_event *event) { /* padding has a NULL time_delta */ event->type_len = RINGBUF_TYPE_PADDING; event->time_delta = 0; } static unsigned rb_event_data_length(struct ring_buffer_event *event) { unsigned length; if (event->type_len) length = event->type_len * RB_ALIGNMENT; else length = event->array[0]; return length + RB_EVNT_HDR_SIZE; } /* * Return the length of the given event. Will return * the length of the time extend if the event is a * time extend. */ static inline unsigned rb_event_length(struct ring_buffer_event *event) { switch (event->type_len) { case RINGBUF_TYPE_PADDING: if (rb_null_event(event)) /* undefined */ return -1; return event->array[0] + RB_EVNT_HDR_SIZE; case RINGBUF_TYPE_TIME_EXTEND: return RB_LEN_TIME_EXTEND; case RINGBUF_TYPE_TIME_STAMP: return RB_LEN_TIME_STAMP; case RINGBUF_TYPE_DATA: return rb_event_data_length(event); default: BUG(); } /* not hit */ return 0; } /* * Return total length of time extend and data, * or just the event length for all other events. */ static inline unsigned rb_event_ts_length(struct ring_buffer_event *event) { unsigned len = 0; if (extended_time(event)) { /* time extends include the data event after it */ len = RB_LEN_TIME_EXTEND; event = skip_time_extend(event); } return len + rb_event_length(event); } /** * ring_buffer_event_length - return the length of the event * @event: the event to get the length of * * Returns the size of the data load of a data event. * If the event is something other than a data event, it * returns the size of the event itself. With the exception * of a TIME EXTEND, where it still returns the size of the * data load of the data event after it. */ unsigned ring_buffer_event_length(struct ring_buffer_event *event) { unsigned length; if (extended_time(event)) event = skip_time_extend(event); length = rb_event_length(event); if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX) return length; length -= RB_EVNT_HDR_SIZE; if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0])) length -= sizeof(event->array[0]); return length; } EXPORT_SYMBOL_GPL(ring_buffer_event_length); /* inline for ring buffer fast paths */ static __always_inline void * rb_event_data(struct ring_buffer_event *event) { if (extended_time(event)) event = skip_time_extend(event); BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX); /* If length is in len field, then array[0] has the data */ if (event->type_len) return (void *)&event->array[0]; /* Otherwise length is in array[0] and array[1] has the data */ return (void *)&event->array[1]; } /** * ring_buffer_event_data - return the data of the event * @event: the event to get the data from */ void *ring_buffer_event_data(struct ring_buffer_event *event) { return rb_event_data(event); } EXPORT_SYMBOL_GPL(ring_buffer_event_data); #define for_each_buffer_cpu(buffer, cpu) \ for_each_cpu(cpu, buffer->cpumask) #define TS_SHIFT 27 #define TS_MASK ((1ULL << TS_SHIFT) - 1) #define TS_DELTA_TEST (~TS_MASK) /** * ring_buffer_event_time_stamp - return the event's extended timestamp * @event: the event to get the timestamp of * * Returns the extended timestamp associated with a data event. * An extended time_stamp is a 64-bit timestamp represented * internally in a special way that makes the best use of space * contained within a ring buffer event. This function decodes * it and maps it to a straight u64 value. */ u64 ring_buffer_event_time_stamp(struct ring_buffer_event *event) { u64 ts; ts = event->array[0]; ts <<= TS_SHIFT; ts += event->time_delta; return ts; } /* Flag when events were overwritten */ #define RB_MISSED_EVENTS (1 << 31) /* Missed count stored at end */ #define RB_MISSED_STORED (1 << 30) #define RB_MISSED_FLAGS (RB_MISSED_EVENTS|RB_MISSED_STORED) struct buffer_data_page { u64 time_stamp; /* page time stamp */ local_t commit; /* write committed index */ unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */ }; /* * Note, the buffer_page list must be first. The buffer pages * are allocated in cache lines, which means that each buffer * page will be at the beginning of a cache line, and thus * the least significant bits will be zero. We use this to * add flags in the list struct pointers, to make the ring buffer * lockless. */ struct buffer_page { struct list_head list; /* list of buffer pages */ local_t write; /* index for next write */ unsigned read; /* index for next read */ local_t entries; /* entries on this page */ unsigned long real_end; /* real end of data */ struct buffer_data_page *page; /* Actual data page */ }; /* * The buffer page counters, write and entries, must be reset * atomically when crossing page boundaries. To synchronize this * update, two counters are inserted into the number. One is * the actual counter for the write position or count on the page. * * The other is a counter of updaters. Before an update happens * the update partition of the counter is incremented. This will * allow the updater to update the counter atomically. * * The counter is 20 bits, and the state data is 12. */ #define RB_WRITE_MASK 0xfffff #define RB_WRITE_INTCNT (1 << 20) static void rb_init_page(struct buffer_data_page *bpage) { local_set(&bpage->commit, 0); } /** * ring_buffer_page_len - the size of data on the page. * @page: The page to read * * Returns the amount of data on the page, including buffer page header. */ size_t ring_buffer_page_len(void *page) { struct buffer_data_page *bpage = page; return (local_read(&bpage->commit) & ~RB_MISSED_FLAGS) + BUF_PAGE_HDR_SIZE; } /* * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing * this issue out. */ static void free_buffer_page(struct buffer_page *bpage) { free_page((unsigned long)bpage->page); kfree(bpage); } /* * We need to fit the time_stamp delta into 27 bits. */ static inline int test_time_stamp(u64 delta) { if (delta & TS_DELTA_TEST) return 1; return 0; } #define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE) /* Max payload is BUF_PAGE_SIZE - header (8bytes) */ #define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2)) int ring_buffer_print_page_header(struct trace_seq *s) { struct buffer_data_page field; trace_seq_printf(s, "\tfield: u64 timestamp;\t" "offset:0;\tsize:%u;\tsigned:%u;\n", (unsigned int)sizeof(field.time_stamp), (unsigned int)is_signed_type(u64)); trace_seq_printf(s, "\tfield: local_t commit;\t" "offset:%u;\tsize:%u;\tsigned:%u;\n", (unsigned int)offsetof(typeof(field), commit), (unsigned int)sizeof(field.commit), (unsigned int)is_signed_type(long)); trace_seq_printf(s, "\tfield: int overwrite;\t" "offset:%u;\tsize:%u;\tsigned:%u;\n", (unsigned int)offsetof(typeof(field), commit), 1, (unsigned int)is_signed_type(long)); trace_seq_printf(s, "\tfield: char data;\t" "offset:%u;\tsize:%u;\tsigned:%u;\n", (unsigned int)offsetof(typeof(field), data), (unsigned int)BUF_PAGE_SIZE, (unsigned int)is_signed_type(char)); return !trace_seq_has_overflowed(s); } struct rb_irq_work { struct irq_work work; wait_queue_head_t waiters; wait_queue_head_t full_waiters; bool waiters_pending; bool full_waiters_pending; bool wakeup_full; }; /* * Structure to hold event state and handle nested events. */ struct rb_event_info { u64 ts; u64 delta; unsigned long length; struct buffer_page *tail_page; int add_timestamp; }; /* * Used for which event context the event is in. * NMI = 0 * IRQ = 1 * SOFTIRQ = 2 * NORMAL = 3 * * See trace_recursive_lock() comment below for more details. */ enum { RB_CTX_NMI, RB_CTX_IRQ, RB_CTX_SOFTIRQ, RB_CTX_NORMAL, RB_CTX_MAX }; /* * head_page == tail_page && head == tail then buffer is empty. */ struct ring_buffer_per_cpu { int cpu; atomic_t record_disabled; struct ring_buffer *buffer; raw_spinlock_t reader_lock; /* serialize readers */ arch_spinlock_t lock; struct lock_class_key lock_key; struct buffer_data_page *free_page; unsigned long nr_pages; unsigned int current_context; struct list_head *pages; struct buffer_page *head_page; /* read from head */ struct buffer_page *tail_page; /* write to tail */ struct buffer_page *commit_page; /* committed pages */ struct buffer_page *reader_page; unsigned long lost_events; unsigned long last_overrun; unsigned long nest; local_t entries_bytes; local_t entries; local_t overrun; local_t commit_overrun; local_t dropped_events; local_t committing; local_t commits; unsigned long read; unsigned long read_bytes; u64 write_stamp; u64 read_stamp; /* ring buffer pages to update, > 0 to add, < 0 to remove */ long nr_pages_to_update; struct list_head new_pages; /* new pages to add */ struct work_struct update_pages_work; struct completion update_done; struct rb_irq_work irq_work; }; struct ring_buffer { unsigned flags; int cpus; atomic_t record_disabled; atomic_t resize_disabled; cpumask_var_t cpumask; struct lock_class_key *reader_lock_key; struct mutex mutex; struct ring_buffer_per_cpu **buffers; struct hlist_node node; u64 (*clock)(void); struct rb_irq_work irq_work; bool time_stamp_abs; }; struct ring_buffer_iter { struct ring_buffer_per_cpu *cpu_buffer; unsigned long head; struct buffer_page *head_page; struct buffer_page *cache_reader_page; unsigned long cache_read; u64 read_stamp; }; /* * rb_wake_up_waiters - wake up tasks waiting for ring buffer input * * Schedules a delayed work to wake up any task that is blocked on the * ring buffer waiters queue. */ static void rb_wake_up_waiters(struct irq_work *work) { struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work); wake_up_all(&rbwork->waiters); if (rbwork->wakeup_full) { rbwork->wakeup_full = false; wake_up_all(&rbwork->full_waiters); } } /** * ring_buffer_wait - wait for input to the ring buffer * @buffer: buffer to wait on * @cpu: the cpu buffer to wait on * @full: wait until a full page is available, if @cpu != RING_BUFFER_ALL_CPUS * * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon * as data is added to any of the @buffer's cpu buffers. Otherwise * it will wait for data to be added to a specific cpu buffer. */ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full) { struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer); DEFINE_WAIT(wait); struct rb_irq_work *work; int ret = 0; /* * Depending on what the caller is waiting for, either any * data in any cpu buffer, or a specific buffer, put the * caller on the appropriate wait queue. */ if (cpu == RING_BUFFER_ALL_CPUS) { work = &buffer->irq_work; /* Full only makes sense on per cpu reads */ full = false; } else { if (!cpumask_test_cpu(cpu, buffer->cpumask)) return -ENODEV; cpu_buffer = buffer->buffers[cpu]; work = &cpu_buffer->irq_work; } while (true) { if (full) prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE); else prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE); /* * The events can happen in critical sections where * checking a work queue can cause deadlocks. * After adding a task to the queue, this flag is set * only to notify events to try to wake up the queue * using irq_work. * * We don't clear it even if the buffer is no longer * empty. The flag only causes the next event to run * irq_work to do the work queue wake up. The worse * that can happen if we race with !trace_empty() is that * an event will cause an irq_work to try to wake up * an empty queue. * * There's no reason to protect this flag either, as * the work queue and irq_work logic will do the necessary * synchronization for the wake ups. The only thing * that is necessary is that the wake up happens after * a task has been queued. It's OK for spurious wake ups. */ if (full) work->full_waiters_pending = true; else work->waiters_pending = true; if (signal_pending(current)) { ret = -EINTR; break; } if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) break; if (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)) { unsigned long flags; bool pagebusy; if (!full) break; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page; raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); if (!pagebusy) break; } schedule(); } if (full) finish_wait(&work->full_waiters, &wait); else finish_wait(&work->waiters, &wait); return ret; } /** * ring_buffer_poll_wait - poll on buffer input * @buffer: buffer to wait on * @cpu: the cpu buffer to wait on * @filp: the file descriptor * @poll_table: The poll descriptor * * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon * as data is added to any of the @buffer's cpu buffers. Otherwise * it will wait for data to be added to a specific cpu buffer. * * Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers, * zero otherwise. */ __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu, struct file *filp, poll_table *poll_table) { struct ring_buffer_per_cpu *cpu_buffer; struct rb_irq_work *work; if (cpu == RING_BUFFER_ALL_CPUS) work = &buffer->irq_work; else { if (!cpumask_test_cpu(cpu, buffer->cpumask)) return -EINVAL; cpu_buffer = buffer->buffers[cpu]; work = &cpu_buffer->irq_work; } poll_wait(filp, &work->waiters, poll_table); work->waiters_pending = true; /* * There's a tight race between setting the waiters_pending and * checking if the ring buffer is empty. Once the waiters_pending bit * is set, the next event will wake the task up, but we can get stuck * if there's only a single event in. * * FIXME: Ideally, we need a memory barrier on the writer side as well, * but adding a memory barrier to all events will cause too much of a * performance hit in the fast path. We only need a memory barrier when * the buffer goes from empty to having content. But as this race is * extremely small, and it's not a problem if another event comes in, we * will fix it later. */ smp_mb(); if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) || (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu))) return EPOLLIN | EPOLLRDNORM; return 0; } /* buffer may be either ring_buffer or ring_buffer_per_cpu */ #define RB_WARN_ON(b, cond) \ ({ \ int _____ret = unlikely(cond); \ if (_____ret) { \ if (__same_type(*(b), struct ring_buffer_per_cpu)) { \ struct ring_buffer_per_cpu *__b = \ (void *)b; \ atomic_inc(&__b->buffer->record_disabled); \ } else \ atomic_inc(&b->record_disabled); \ WARN_ON(1); \ } \ _____ret; \ }) /* Up this if you want to test the TIME_EXTENTS and normalization */ #define DEBUG_SHIFT 0 static inline u64 rb_time_stamp(struct ring_buffer *buffer) { /* shift to debug/test normalization and TIME_EXTENTS */ return buffer->clock() << DEBUG_SHIFT; } u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu) { u64 time; preempt_disable_notrace(); time = rb_time_stamp(buffer); preempt_enable_no_resched_notrace(); return time; } EXPORT_SYMBOL_GPL(ring_buffer_time_stamp); void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer, int cpu, u64 *ts) { /* Just stupid testing the normalize function and deltas */ *ts >>= DEBUG_SHIFT; } EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp); /* * Making the ring buffer lockless makes things tricky. * Although writes only happen on the CPU that they are on, * and they only need to worry about interrupts. Reads can * happen on any CPU. * * The reader page is always off the ring buffer, but when the * reader finishes with a page, it needs to swap its page with * a new one from the buffer. The reader needs to take from * the head (writes go to the tail). But if a writer is in overwrite * mode and wraps, it must push the head page forward. * * Here lies the problem. * * The reader must be careful to replace only the head page, and * not another one. As described at the top of the file in the * ASCII art, the reader sets its old page to point to the next * page after head. It then sets the page after head to point to * the old reader page. But if the writer moves the head page * during this operation, the reader could end up with the tail. * * We use cmpxchg to help prevent this race. We also do something * special with the page before head. We set the LSB to 1. * * When the writer must push the page forward, it will clear the * bit that points to the head page, move the head, and then set * the bit that points to the new head page. * * We also don't want an interrupt coming in and moving the head * page on another writer. Thus we use the second LSB to catch * that too. Thus: * * head->list->prev->next bit 1 bit 0 * ------- ------- * Normal page 0 0 * Points to head page 0 1 * New head page 1 0 * * Note we can not trust the prev pointer of the head page, because: * * +----+ +-----+ +-----+ * | |------>| T |---X--->| N | * | |<------| | | | * +----+ +-----+ +-----+ * ^ ^ | * | +-----+ | | * +----------| R |----------+ | * | |<-----------+ * +-----+ * * Key: ---X--> HEAD flag set in pointer * T Tail page * R Reader page * N Next page * * (see __rb_reserve_next() to see where this happens) * * What the above shows is that the reader just swapped out * the reader page with a page in the buffer, but before it * could make the new header point back to the new page added * it was preempted by a writer. The writer moved forward onto * the new page added by the reader and is about to move forward * again. * * You can see, it is legitimate for the previous pointer of * the head (or any page) not to point back to itself. But only * temporarily. */ #define RB_PAGE_NORMAL 0UL #define RB_PAGE_HEAD 1UL #define RB_PAGE_UPDATE 2UL #define RB_FLAG_MASK 3UL /* PAGE_MOVED is not part of the mask */ #define RB_PAGE_MOVED 4UL /* * rb_list_head - remove any bit */ static struct list_head *rb_list_head(struct list_head *list) { unsigned long val = (unsigned long)list; return (struct list_head *)(val & ~RB_FLAG_MASK); } /* * rb_is_head_page - test if the given page is the head page * * Because the reader may move the head_page pointer, we can * not trust what the head page is (it may be pointing to * the reader page). But if the next page is a header page, * its flags will be non zero. */ static inline int rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *page, struct list_head *list) { unsigned long val; val = (unsigned long)list->next; if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list) return RB_PAGE_MOVED; return val & RB_FLAG_MASK; } /* * rb_is_reader_page * * The unique thing about the reader page, is that, if the * writer is ever on it, the previous pointer never points * back to the reader page. */ static bool rb_is_reader_page(struct buffer_page *page) { struct list_head *list = page->list.prev; return rb_list_head(list->next) != &page->list; } /* * rb_set_list_to_head - set a list_head to be pointing to head. */ static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer, struct list_head *list) { unsigned long *ptr; ptr = (unsigned long *)&list->next; *ptr |= RB_PAGE_HEAD; *ptr &= ~RB_PAGE_UPDATE; } /* * rb_head_page_activate - sets up head page */ static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer) { struct buffer_page *head; head = cpu_buffer->head_page; if (!head) return; /* * Set the previous list pointer to have the HEAD flag. */ rb_set_list_to_head(cpu_buffer, head->list.prev); } static void rb_list_head_clear(struct list_head *list) { unsigned long *ptr = (unsigned long *)&list->next; *ptr &= ~RB_FLAG_MASK; } /* * rb_head_page_deactivate - clears head page ptr (for free list) */ static void rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer) { struct list_head *hd; /* Go through the whole list and clear any pointers found. */ rb_list_head_clear(cpu_buffer->pages); list_for_each(hd, cpu_buffer->pages) rb_list_head_clear(hd); } static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *head, struct buffer_page *prev, int old_flag, int new_flag) { struct list_head *list; unsigned long val = (unsigned long)&head->list; unsigned long ret; list = &prev->list; val &= ~RB_FLAG_MASK; ret = cmpxchg((unsigned long *)&list->next, val | old_flag, val | new_flag); /* check if the reader took the page */ if ((ret & ~RB_FLAG_MASK) != val) return RB_PAGE_MOVED; return ret & RB_FLAG_MASK; } static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *head, struct buffer_page *prev, int old_flag) { return rb_head_page_set(cpu_buffer, head, prev, old_flag, RB_PAGE_UPDATE); } static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *head, struct buffer_page *prev, int old_flag) { return rb_head_page_set(cpu_buffer, head, prev, old_flag, RB_PAGE_HEAD); } static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *head, struct buffer_page *prev, int old_flag) { return rb_head_page_set(cpu_buffer, head, prev, old_flag, RB_PAGE_NORMAL); } static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page **bpage) { struct list_head *p = rb_list_head((*bpage)->list.next); *bpage = list_entry(p, struct buffer_page, list); } static struct buffer_page * rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer) { struct buffer_page *head; struct buffer_page *page; struct list_head *list; int i; if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page)) return NULL; /* sanity check */ list = cpu_buffer->pages; if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list)) return NULL; page = head = cpu_buffer->head_page; /* * It is possible that the writer moves the header behind * where we started, and we miss in one loop. * A second loop should grab the header, but we'll do * three loops just because I'm paranoid. */ for (i = 0; i < 3; i++) { do { if (rb_is_head_page(cpu_buffer, page, page->list.prev)) { cpu_buffer->head_page = page; return page; } rb_inc_page(cpu_buffer, &page); } while (page != head); } RB_WARN_ON(cpu_buffer, 1); return NULL; } static int rb_head_page_replace(struct buffer_page *old, struct buffer_page *new) { unsigned long *ptr = (unsigned long *)&old->list.prev->next; unsigned long val; unsigned long ret; val = *ptr & ~RB_FLAG_MASK; val |= RB_PAGE_HEAD; ret = cmpxchg(ptr, val, (unsigned long)&new->list); return ret == val; } /* * rb_tail_page_update - move the tail page forward */ static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *tail_page, struct buffer_page *next_page) { unsigned long old_entries; unsigned long old_write; /* * The tail page now needs to be moved forward. * * We need to reset the tail page, but without messing * with possible erasing of data brought in by interrupts * that have moved the tail page and are currently on it. * * We add a counter to the write field to denote this. */ old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write); old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries); /* * Just make sure we have seen our old_write and synchronize * with any interrupts that come in. */ barrier(); /* * If the tail page is still the same as what we think * it is, then it is up to us to update the tail * pointer. */ if (tail_page == READ_ONCE(cpu_buffer->tail_page)) { /* Zero the write counter */ unsigned long val = old_write & ~RB_WRITE_MASK; unsigned long eval = old_entries & ~RB_WRITE_MASK; /* * This will only succeed if an interrupt did * not come in and change it. In which case, we * do not want to modify it. * * We add (void) to let the compiler know that we do not care * about the return value of these functions. We use the * cmpxchg to only update if an interrupt did not already * do it for us. If the cmpxchg fails, we don't care. */ (void)local_cmpxchg(&next_page->write, old_write, val); (void)local_cmpxchg(&next_page->entries, old_entries, eval); /* * No need to worry about races with clearing out the commit. * it only can increment when a commit takes place. But that * only happens in the outer most nested commit. */ local_set(&next_page->page->commit, 0); /* Again, either we update tail_page or an interrupt does */ (void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page); } } static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *bpage) { unsigned long val = (unsigned long)bpage; if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK)) return 1; return 0; } /** * rb_check_list - make sure a pointer to a list has the last bits zero */ static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer, struct list_head *list) { if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev)) return 1; if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next)) return 1; return 0; } /** * rb_check_pages - integrity check of buffer pages * @cpu_buffer: CPU buffer with pages to test * * As a safety measure we check to make sure the data pages have not * been corrupted. */ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer) { struct list_head *head = cpu_buffer->pages; struct buffer_page *bpage, *tmp; /* Reset the head page if it exists */ if (cpu_buffer->head_page) rb_set_head_page(cpu_buffer); rb_head_page_deactivate(cpu_buffer); if (RB_WARN_ON(cpu_buffer, head->next->prev != head)) return -1; if (RB_WARN_ON(cpu_buffer, head->prev->next != head)) return -1; if (rb_check_list(cpu_buffer, head)) return -1; list_for_each_entry_safe(bpage, tmp, head, list) { if (RB_WARN_ON(cpu_buffer, bpage->list.next->prev != &bpage->list)) return -1; if (RB_WARN_ON(cpu_buffer, bpage->list.prev->next != &bpage->list)) return -1; if (rb_check_list(cpu_buffer, &bpage->list)) return -1; } rb_head_page_activate(cpu_buffer); return 0; } static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu) { struct buffer_page *bpage, *tmp; bool user_thread = current->mm != NULL; gfp_t mflags; long i; /* * Check if the available memory is there first. * Note, si_mem_available() only gives us a rough estimate of available * memory. It may not be accurate. But we don't care, we just want * to prevent doing any allocation when it is obvious that it is * not going to succeed. */ i = si_mem_available(); if (i < nr_pages) return -ENOMEM; /* * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails * gracefully without invoking oom-killer and the system is not * destabilized. */ mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL; /* * If a user thread allocates too much, and si_mem_available() * reports there's enough memory, even though there is not. * Make sure the OOM killer kills this thread. This can happen * even with RETRY_MAYFAIL because another task may be doing * an allocation after this task has taken all memory. * This is the task the OOM killer needs to take out during this * loop, even if it was triggered by an allocation somewhere else. */ if (user_thread) set_current_oom_origin(); for (i = 0; i < nr_pages; i++) { struct page *page; bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), mflags, cpu_to_node(cpu)); if (!bpage) goto free_pages; list_add(&bpage->list, pages); page = alloc_pages_node(cpu_to_node(cpu), mflags, 0); if (!page) goto free_pages; bpage->page = page_address(page); rb_init_page(bpage->page); if (user_thread && fatal_signal_pending(current)) goto free_pages; } if (user_thread) clear_current_oom_origin(); return 0; free_pages: list_for_each_entry_safe(bpage, tmp, pages, list) { list_del_init(&bpage->list); free_buffer_page(bpage); } if (user_thread) clear_current_oom_origin(); return -ENOMEM; } static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages) { LIST_HEAD(pages); WARN_ON(!nr_pages); if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu)) return -ENOMEM; /* * The ring buffer page list is a circular list that does not * start and end with a list head. All page list items point to * other pages. */ cpu_buffer->pages = pages.next; list_del(&pages); cpu_buffer->nr_pages = nr_pages; rb_check_pages(cpu_buffer); return 0; } static struct ring_buffer_per_cpu * rb_allocate_cpu_buffer(struct ring_buffer *buffer, long nr_pages, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; struct buffer_page *bpage; struct page *page; int ret; cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu)); if (!cpu_buffer) return NULL; cpu_buffer->cpu = cpu; cpu_buffer->buffer = buffer; raw_spin_lock_init(&cpu_buffer->reader_lock); lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key); cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler); init_completion(&cpu_buffer->update_done); init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters); init_waitqueue_head(&cpu_buffer->irq_work.waiters); init_waitqueue_head(&cpu_buffer->irq_work.full_waiters); bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu)); if (!bpage) goto fail_free_buffer; rb_check_bpage(cpu_buffer, bpage); cpu_buffer->reader_page = bpage; page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0); if (!page) goto fail_free_reader; bpage->page = page_address(page); rb_init_page(bpage->page); INIT_LIST_HEAD(&cpu_buffer->reader_page->list); INIT_LIST_HEAD(&cpu_buffer->new_pages); ret = rb_allocate_pages(cpu_buffer, nr_pages); if (ret < 0) goto fail_free_reader; cpu_buffer->head_page = list_entry(cpu_buffer->pages, struct buffer_page, list); cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page; rb_head_page_activate(cpu_buffer); return cpu_buffer; fail_free_reader: free_buffer_page(cpu_buffer->reader_page); fail_free_buffer: kfree(cpu_buffer); return NULL; } static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer) { struct list_head *head = cpu_buffer->pages; struct buffer_page *bpage, *tmp; free_buffer_page(cpu_buffer->reader_page); rb_head_page_deactivate(cpu_buffer); if (head) { list_for_each_entry_safe(bpage, tmp, head, list) { list_del_init(&bpage->list); free_buffer_page(bpage); } bpage = list_entry(head, struct buffer_page, list); free_buffer_page(bpage); } kfree(cpu_buffer); } /** * __ring_buffer_alloc - allocate a new ring_buffer * @size: the size in bytes per cpu that is needed. * @flags: attributes to set for the ring buffer. * * Currently the only flag that is available is the RB_FL_OVERWRITE * flag. This flag means that the buffer will overwrite old data * when the buffer wraps. If this flag is not set, the buffer will * drop data when the tail hits the head. */ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key) { struct ring_buffer *buffer; long nr_pages; int bsize; int cpu; int ret; /* keep it in its own cache line */ buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()), GFP_KERNEL); if (!buffer) return NULL; if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL)) goto fail_free_buffer; nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE); buffer->flags = flags; buffer->clock = trace_clock_local; buffer->reader_lock_key = key; init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters); init_waitqueue_head(&buffer->irq_work.waiters); /* need at least two pages */ if (nr_pages < 2) nr_pages = 2; buffer->cpus = nr_cpu_ids; bsize = sizeof(void *) * nr_cpu_ids; buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()), GFP_KERNEL); if (!buffer->buffers) goto fail_free_cpumask; cpu = raw_smp_processor_id(); cpumask_set_cpu(cpu, buffer->cpumask); buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) goto fail_free_buffers; ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node); if (ret < 0) goto fail_free_buffers; mutex_init(&buffer->mutex); return buffer; fail_free_buffers: for_each_buffer_cpu(buffer, cpu) { if (buffer->buffers[cpu]) rb_free_cpu_buffer(buffer->buffers[cpu]); } kfree(buffer->buffers); fail_free_cpumask: free_cpumask_var(buffer->cpumask); fail_free_buffer: kfree(buffer); return NULL; } EXPORT_SYMBOL_GPL(__ring_buffer_alloc); /** * ring_buffer_free - free a ring buffer. * @buffer: the buffer to free. */ void ring_buffer_free(struct ring_buffer *buffer) { int cpu; cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node); for_each_buffer_cpu(buffer, cpu) rb_free_cpu_buffer(buffer->buffers[cpu]); kfree(buffer->buffers); free_cpumask_var(buffer->cpumask); kfree(buffer); } EXPORT_SYMBOL_GPL(ring_buffer_free); void ring_buffer_set_clock(struct ring_buffer *buffer, u64 (*clock)(void)) { buffer->clock = clock; } void ring_buffer_set_time_stamp_abs(struct ring_buffer *buffer, bool abs) { buffer->time_stamp_abs = abs; } bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer) { return buffer->time_stamp_abs; } static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer); static inline unsigned long rb_page_entries(struct buffer_page *bpage) { return local_read(&bpage->entries) & RB_WRITE_MASK; } static inline unsigned long rb_page_write(struct buffer_page *bpage) { return local_read(&bpage->write) & RB_WRITE_MASK; } static int rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages) { struct list_head *tail_page, *to_remove, *next_page; struct buffer_page *to_remove_page, *tmp_iter_page; struct buffer_page *last_page, *first_page; unsigned long nr_removed; unsigned long head_bit; int page_entries; head_bit = 0; raw_spin_lock_irq(&cpu_buffer->reader_lock); atomic_inc(&cpu_buffer->record_disabled); /* * We don't race with the readers since we have acquired the reader * lock. We also don't race with writers after disabling recording. * This makes it easy to figure out the first and the last page to be * removed from the list. We unlink all the pages in between including * the first and last pages. This is done in a busy loop so that we * lose the least number of traces. * The pages are freed after we restart recording and unlock readers. */ tail_page = &cpu_buffer->tail_page->list; /* * tail page might be on reader page, we remove the next page * from the ring buffer */ if (cpu_buffer->tail_page == cpu_buffer->reader_page) tail_page = rb_list_head(tail_page->next); to_remove = tail_page; /* start of pages to remove */ first_page = list_entry(rb_list_head(to_remove->next), struct buffer_page, list); for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) { to_remove = rb_list_head(to_remove)->next; head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD; } next_page = rb_list_head(to_remove)->next; /* * Now we remove all pages between tail_page and next_page. * Make sure that we have head_bit value preserved for the * next page */ tail_page->next = (struct list_head *)((unsigned long)next_page | head_bit); next_page = rb_list_head(next_page); next_page->prev = tail_page; /* make sure pages points to a valid page in the ring buffer */ cpu_buffer->pages = next_page; /* update head page */ if (head_bit) cpu_buffer->head_page = list_entry(next_page, struct buffer_page, list); /* * change read pointer to make sure any read iterators reset * themselves */ cpu_buffer->read = 0; /* pages are removed, resume tracing and then free the pages */ atomic_dec(&cpu_buffer->record_disabled); raw_spin_unlock_irq(&cpu_buffer->reader_lock); RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)); /* last buffer page to remove */ last_page = list_entry(rb_list_head(to_remove), struct buffer_page, list); tmp_iter_page = first_page; do { cond_resched(); to_remove_page = tmp_iter_page; rb_inc_page(cpu_buffer, &tmp_iter_page); /* update the counters */ page_entries = rb_page_entries(to_remove_page); if (page_entries) { /* * If something was added to this page, it was full * since it is not the tail page. So we deduct the * bytes consumed in ring buffer from here. * Increment overrun to account for the lost events. */ local_add(page_entries, &cpu_buffer->overrun); local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes); } /* * We have already removed references to this list item, just * free up the buffer_page and its page */ free_buffer_page(to_remove_page); nr_removed--; } while (to_remove_page != last_page); RB_WARN_ON(cpu_buffer, nr_removed); return nr_removed == 0; } static int rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer) { struct list_head *pages = &cpu_buffer->new_pages; int retries, success; raw_spin_lock_irq(&cpu_buffer->reader_lock); /* * We are holding the reader lock, so the reader page won't be swapped * in the ring buffer. Now we are racing with the writer trying to * move head page and the tail page. * We are going to adapt the reader page update process where: * 1. We first splice the start and end of list of new pages between * the head page and its previous page. * 2. We cmpxchg the prev_page->next to point from head page to the * start of new pages list. * 3. Finally, we update the head->prev to the end of new list. * * We will try this process 10 times, to make sure that we don't keep * spinning. */ retries = 10; success = 0; while (retries--) { struct list_head *head_page, *prev_page, *r; struct list_head *last_page, *first_page; struct list_head *head_page_with_bit; head_page = &rb_set_head_page(cpu_buffer)->list; if (!head_page) break; prev_page = head_page->prev; first_page = pages->next; last_page = pages->prev; head_page_with_bit = (struct list_head *) ((unsigned long)head_page | RB_PAGE_HEAD); last_page->next = head_page_with_bit; first_page->prev = prev_page; r = cmpxchg(&prev_page->next, head_page_with_bit, first_page); if (r == head_page_with_bit) { /* * yay, we replaced the page pointer to our new list, * now, we just have to update to head page's prev * pointer to point to end of list */ head_page->prev = last_page; success = 1; break; } } if (success) INIT_LIST_HEAD(pages); /* * If we weren't successful in adding in new pages, warn and stop * tracing */ RB_WARN_ON(cpu_buffer, !success); raw_spin_unlock_irq(&cpu_buffer->reader_lock); /* free pages if they weren't inserted */ if (!success) { struct buffer_page *bpage, *tmp; list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages, list) { list_del_init(&bpage->list); free_buffer_page(bpage); } } return success; } static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer) { int success; if (cpu_buffer->nr_pages_to_update > 0) success = rb_insert_pages(cpu_buffer); else success = rb_remove_pages(cpu_buffer, -cpu_buffer->nr_pages_to_update); if (success) cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update; } static void update_pages_handler(struct work_struct *work) { struct ring_buffer_per_cpu *cpu_buffer = container_of(work, struct ring_buffer_per_cpu, update_pages_work); rb_update_pages(cpu_buffer); complete(&cpu_buffer->update_done); } /** * ring_buffer_resize - resize the ring buffer * @buffer: the buffer to resize. * @size: the new size. * @cpu_id: the cpu buffer to resize * * Minimum size is 2 * BUF_PAGE_SIZE. * * Returns 0 on success and < 0 on failure. */ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size, int cpu_id) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long nr_pages; int cpu, err = 0; /* * Always succeed at resizing a non-existent buffer: */ if (!buffer) return size; /* Make sure the requested buffer exists */ if (cpu_id != RING_BUFFER_ALL_CPUS && !cpumask_test_cpu(cpu_id, buffer->cpumask)) return size; nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE); /* we need a minimum of two pages */ if (nr_pages < 2) nr_pages = 2; size = nr_pages * BUF_PAGE_SIZE; /* * Don't succeed if resizing is disabled, as a reader might be * manipulating the ring buffer and is expecting a sane state while * this is true. */ if (atomic_read(&buffer->resize_disabled)) return -EBUSY; /* prevent another thread from changing buffer sizes */ mutex_lock(&buffer->mutex); if (cpu_id == RING_BUFFER_ALL_CPUS) { /* calculate the pages to update */ for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu]; cpu_buffer->nr_pages_to_update = nr_pages - cpu_buffer->nr_pages; /* * nothing more to do for removing pages or no update */ if (cpu_buffer->nr_pages_to_update <= 0) continue; /* * to add pages, make sure all new pages can be * allocated without receiving ENOMEM */ INIT_LIST_HEAD(&cpu_buffer->new_pages); if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update, &cpu_buffer->new_pages, cpu)) { /* not enough memory for new pages */ err = -ENOMEM; goto out_err; } } get_online_cpus(); /* * Fire off all the required work handlers * We can't schedule on offline CPUs, but it's not necessary * since we can change their buffer sizes without any race. */ for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu]; if (!cpu_buffer->nr_pages_to_update) continue; /* Can't run something on an offline CPU. */ if (!cpu_online(cpu)) { rb_update_pages(cpu_buffer); cpu_buffer->nr_pages_to_update = 0; } else { schedule_work_on(cpu, &cpu_buffer->update_pages_work); } } /* wait for all the updates to complete */ for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu]; if (!cpu_buffer->nr_pages_to_update) continue; if (cpu_online(cpu)) wait_for_completion(&cpu_buffer->update_done); cpu_buffer->nr_pages_to_update = 0; } put_online_cpus(); } else { /* Make sure this CPU has been initialized */ if (!cpumask_test_cpu(cpu_id, buffer->cpumask)) goto out; cpu_buffer = buffer->buffers[cpu_id]; if (nr_pages == cpu_buffer->nr_pages) goto out; cpu_buffer->nr_pages_to_update = nr_pages - cpu_buffer->nr_pages; INIT_LIST_HEAD(&cpu_buffer->new_pages); if (cpu_buffer->nr_pages_to_update > 0 && __rb_allocate_pages(cpu_buffer->nr_pages_to_update, &cpu_buffer->new_pages, cpu_id)) { err = -ENOMEM; goto out_err; } get_online_cpus(); /* Can't run something on an offline CPU. */ if (!cpu_online(cpu_id)) rb_update_pages(cpu_buffer); else { schedule_work_on(cpu_id, &cpu_buffer->update_pages_work); wait_for_completion(&cpu_buffer->update_done); } cpu_buffer->nr_pages_to_update = 0; put_online_cpus(); } out: /* * The ring buffer resize can happen with the ring buffer * enabled, so that the update disturbs the tracing as little * as possible. But if the buffer is disabled, we do not need * to worry about that, and we can take the time to verify * that the buffer is not corrupt. */ if (atomic_read(&buffer->record_disabled)) { atomic_inc(&buffer->record_disabled); /* * Even though the buffer was disabled, we must make sure * that it is truly disabled before calling rb_check_pages. * There could have been a race between checking * record_disable and incrementing it. */ synchronize_sched(); for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu]; rb_check_pages(cpu_buffer); } atomic_dec(&buffer->record_disabled); } mutex_unlock(&buffer->mutex); return size; out_err: for_each_buffer_cpu(buffer, cpu) { struct buffer_page *bpage, *tmp; cpu_buffer = buffer->buffers[cpu]; cpu_buffer->nr_pages_to_update = 0; if (list_empty(&cpu_buffer->new_pages)) continue; list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages, list) { list_del_init(&bpage->list); free_buffer_page(bpage); } } mutex_unlock(&buffer->mutex); return err; } EXPORT_SYMBOL_GPL(ring_buffer_resize); void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val) { mutex_lock(&buffer->mutex); if (val) buffer->flags |= RB_FL_OVERWRITE; else buffer->flags &= ~RB_FL_OVERWRITE; mutex_unlock(&buffer->mutex); } EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite); static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index) { return bpage->page->data + index; } static __always_inline struct ring_buffer_event * rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer) { return __rb_page_index(cpu_buffer->reader_page, cpu_buffer->reader_page->read); } static __always_inline struct ring_buffer_event * rb_iter_head_event(struct ring_buffer_iter *iter) { return __rb_page_index(iter->head_page, iter->head); } static __always_inline unsigned rb_page_commit(struct buffer_page *bpage) { return local_read(&bpage->page->commit); } /* Size is determined by what has been committed */ static __always_inline unsigned rb_page_size(struct buffer_page *bpage) { return rb_page_commit(bpage); } static __always_inline unsigned rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer) { return rb_page_commit(cpu_buffer->commit_page); } static __always_inline unsigned rb_event_index(struct ring_buffer_event *event) { unsigned long addr = (unsigned long)event; return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE; } static void rb_inc_iter(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; /* * The iterator could be on the reader page (it starts there). * But the head could have moved, since the reader was * found. Check for this case and assign the iterator * to the head page instead of next. */ if (iter->head_page == cpu_buffer->reader_page) iter->head_page = rb_set_head_page(cpu_buffer); else rb_inc_page(cpu_buffer, &iter->head_page); iter->read_stamp = iter->head_page->page->time_stamp; iter->head = 0; } /* * rb_handle_head_page - writer hit the head page * * Returns: +1 to retry page * 0 to continue * -1 on error */ static int rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer, struct buffer_page *tail_page, struct buffer_page *next_page) { struct buffer_page *new_head; int entries; int type; int ret; entries = rb_page_entries(next_page); /* * The hard part is here. We need to move the head * forward, and protect against both readers on * other CPUs and writers coming in via interrupts. */ type = rb_head_page_set_update(cpu_buffer, next_page, tail_page, RB_PAGE_HEAD); /* * type can be one of four: * NORMAL - an interrupt already moved it for us * HEAD - we are the first to get here. * UPDATE - we are the interrupt interrupting * a current move. * MOVED - a reader on another CPU moved the next * pointer to its reader page. Give up * and try again. */ switch (type) { case RB_PAGE_HEAD: /* * We changed the head to UPDATE, thus * it is our responsibility to update * the counters. */ local_add(entries, &cpu_buffer->overrun); local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes); /* * The entries will be zeroed out when we move the * tail page. */ /* still more to do */ break; case RB_PAGE_UPDATE: /* * This is an interrupt that interrupt the * previous update. Still more to do. */ break; case RB_PAGE_NORMAL: /* * An interrupt came in before the update * and processed this for us. * Nothing left to do. */ return 1; case RB_PAGE_MOVED: /* * The reader is on another CPU and just did * a swap with our next_page. * Try again. */ return 1; default: RB_WARN_ON(cpu_buffer, 1); /* WTF??? */ return -1; } /* * Now that we are here, the old head pointer is * set to UPDATE. This will keep the reader from * swapping the head page with the reader page. * The reader (on another CPU) will spin till * we are finished. * * We just need to protect against interrupts * doing the job. We will set the next pointer * to HEAD. After that, we set the old pointer * to NORMAL, but only if it was HEAD before. * otherwise we are an interrupt, and only * want the outer most commit to reset it. */ new_head = next_page; rb_inc_page(cpu_buffer, &new_head); ret = rb_head_page_set_head(cpu_buffer, new_head, next_page, RB_PAGE_NORMAL); /* * Valid returns are: * HEAD - an interrupt came in and already set it. * NORMAL - One of two things: * 1) We really set it. * 2) A bunch of interrupts came in and moved * the page forward again. */ switch (ret) { case RB_PAGE_HEAD: case RB_PAGE_NORMAL: /* OK */ break; default: RB_WARN_ON(cpu_buffer, 1); return -1; } /* * It is possible that an interrupt came in, * set the head up, then more interrupts came in * and moved it again. When we get back here, * the page would have been set to NORMAL but we * just set it back to HEAD. * * How do you detect this? Well, if that happened * the tail page would have moved. */ if (ret == RB_PAGE_NORMAL) { struct buffer_page *buffer_tail_page; buffer_tail_page = READ_ONCE(cpu_buffer->tail_page); /* * If the tail had moved passed next, then we need * to reset the pointer. */ if (buffer_tail_page != tail_page && buffer_tail_page != next_page) rb_head_page_set_normal(cpu_buffer, new_head, next_page, RB_PAGE_HEAD); } /* * If this was the outer most commit (the one that * changed the original pointer from HEAD to UPDATE), * then it is up to us to reset it to NORMAL. */ if (type == RB_PAGE_HEAD) { ret = rb_head_page_set_normal(cpu_buffer, next_page, tail_page, RB_PAGE_UPDATE); if (RB_WARN_ON(cpu_buffer, ret != RB_PAGE_UPDATE)) return -1; } return 0; } static inline void rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer, unsigned long tail, struct rb_event_info *info) { struct buffer_page *tail_page = info->tail_page; struct ring_buffer_event *event; unsigned long length = info->length; /* * Only the event that crossed the page boundary * must fill the old tail_page with padding. */ if (tail >= BUF_PAGE_SIZE) { /* * If the page was filled, then we still need * to update the real_end. Reset it to zero * and the reader will ignore it. */ if (tail == BUF_PAGE_SIZE) tail_page->real_end = 0; local_sub(length, &tail_page->write); return; } event = __rb_page_index(tail_page, tail); /* account for padding bytes */ local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes); /* * Save the original length to the meta data. * This will be used by the reader to add lost event * counter. */ tail_page->real_end = tail; /* * If this event is bigger than the minimum size, then * we need to be careful that we don't subtract the * write counter enough to allow another writer to slip * in on this page. * We put in a discarded commit instead, to make sure * that this space is not used again. * * If we are less than the minimum size, we don't need to * worry about it. */ if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) { /* No room for any events */ /* Mark the rest of the page with padding */ rb_event_set_padding(event); /* Set the write back to the previous setting */ local_sub(length, &tail_page->write); return; } /* Put in a discarded event */ event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE; event->type_len = RINGBUF_TYPE_PADDING; /* time delta must be non zero */ event->time_delta = 1; /* Set write to end of buffer */ length = (tail + length) - BUF_PAGE_SIZE; local_sub(length, &tail_page->write); } static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer); /* * This is the slow path, force gcc not to inline it. */ static noinline struct ring_buffer_event * rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer, unsigned long tail, struct rb_event_info *info) { struct buffer_page *tail_page = info->tail_page; struct buffer_page *commit_page = cpu_buffer->commit_page; struct ring_buffer *buffer = cpu_buffer->buffer; struct buffer_page *next_page; int ret; next_page = tail_page; rb_inc_page(cpu_buffer, &next_page); /* * If for some reason, we had an interrupt storm that made * it all the way around the buffer, bail, and warn * about it. */ if (unlikely(next_page == commit_page)) { local_inc(&cpu_buffer->commit_overrun); goto out_reset; } /* * This is where the fun begins! * * We are fighting against races between a reader that * could be on another CPU trying to swap its reader * page with the buffer head. * * We are also fighting against interrupts coming in and * moving the head or tail on us as well. * * If the next page is the head page then we have filled * the buffer, unless the commit page is still on the * reader page. */ if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) { /* * If the commit is not on the reader page, then * move the header page. */ if (!rb_is_reader_page(cpu_buffer->commit_page)) { /* * If we are not in overwrite mode, * this is easy, just stop here. */ if (!(buffer->flags & RB_FL_OVERWRITE)) { local_inc(&cpu_buffer->dropped_events); goto out_reset; } ret = rb_handle_head_page(cpu_buffer, tail_page, next_page); if (ret < 0) goto out_reset; if (ret) goto out_again; } else { /* * We need to be careful here too. The * commit page could still be on the reader * page. We could have a small buffer, and * have filled up the buffer with events * from interrupts and such, and wrapped. * * Note, if the tail page is also the on the * reader_page, we let it move out. */ if (unlikely((cpu_buffer->commit_page != cpu_buffer->tail_page) && (cpu_buffer->commit_page == cpu_buffer->reader_page))) { local_inc(&cpu_buffer->commit_overrun); goto out_reset; } } } rb_tail_page_update(cpu_buffer, tail_page, next_page); out_again: rb_reset_tail(cpu_buffer, tail, info); /* Commit what we have for now. */ rb_end_commit(cpu_buffer); /* rb_end_commit() decs committing */ local_inc(&cpu_buffer->committing); /* fail and let the caller try again */ return ERR_PTR(-EAGAIN); out_reset: /* reset write */ rb_reset_tail(cpu_buffer, tail, info); return NULL; } /* Slow path, do not inline */ static noinline struct ring_buffer_event * rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs) { if (abs) event->type_len = RINGBUF_TYPE_TIME_STAMP; else event->type_len = RINGBUF_TYPE_TIME_EXTEND; /* Not the first event on the page, or not delta? */ if (abs || rb_event_index(event)) { event->time_delta = delta & TS_MASK; event->array[0] = delta >> TS_SHIFT; } else { /* nope, just zero it */ event->time_delta = 0; event->array[0] = 0; } return skip_time_extend(event); } static inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event); /** * rb_update_event - update event type and data * @event: the event to update * @type: the type of event * @length: the size of the event field in the ring buffer * * Update the type and data fields of the event. The length * is the actual size that is written to the ring buffer, * and with this, we can determine what to place into the * data field. */ static void rb_update_event(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event, struct rb_event_info *info) { unsigned length = info->length; u64 delta = info->delta; /* Only a commit updates the timestamp */ if (unlikely(!rb_event_is_commit(cpu_buffer, event))) delta = 0; /* * If we need to add a timestamp, then we * add it to the start of the reserved space. */ if (unlikely(info->add_timestamp)) { bool abs = ring_buffer_time_stamp_abs(cpu_buffer->buffer); event = rb_add_time_stamp(event, info->delta, abs); length -= RB_LEN_TIME_EXTEND; delta = 0; } event->time_delta = delta; length -= RB_EVNT_HDR_SIZE; if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) { event->type_len = 0; event->array[0] = length; } else event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT); } static unsigned rb_calculate_event_length(unsigned length) { struct ring_buffer_event event; /* Used only for sizeof array */ /* zero length can cause confusions */ if (!length) length++; if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) length += sizeof(event.array[0]); length += RB_EVNT_HDR_SIZE; length = ALIGN(length, RB_ARCH_ALIGNMENT); /* * In case the time delta is larger than the 27 bits for it * in the header, we need to add a timestamp. If another * event comes in when trying to discard this one to increase * the length, then the timestamp will be added in the allocated * space of this event. If length is bigger than the size needed * for the TIME_EXTEND, then padding has to be used. The events * length must be either RB_LEN_TIME_EXTEND, or greater than or equal * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding. * As length is a multiple of 4, we only need to worry if it * is 12 (RB_LEN_TIME_EXTEND + 4). */ if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT) length += RB_ALIGNMENT; return length; } #ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK static inline bool sched_clock_stable(void) { return true; } #endif static inline int rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event) { unsigned long new_index, old_index; struct buffer_page *bpage; unsigned long index; unsigned long addr; new_index = rb_event_index(event); old_index = new_index + rb_event_ts_length(event); addr = (unsigned long)event; addr &= PAGE_MASK; bpage = READ_ONCE(cpu_buffer->tail_page); if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) { unsigned long write_mask = local_read(&bpage->write) & ~RB_WRITE_MASK; unsigned long event_length = rb_event_length(event); /* * This is on the tail page. It is possible that * a write could come in and move the tail page * and write to the next page. That is fine * because we just shorten what is on this page. */ old_index += write_mask; new_index += write_mask; index = local_cmpxchg(&bpage->write, old_index, new_index); if (index == old_index) { /* update counters */ local_sub(event_length, &cpu_buffer->entries_bytes); return 1; } } /* could not discard */ return 0; } static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer) { local_inc(&cpu_buffer->committing); local_inc(&cpu_buffer->commits); } static __always_inline void rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer) { unsigned long max_count; /* * We only race with interrupts and NMIs on this CPU. * If we own the commit event, then we can commit * all others that interrupted us, since the interruptions * are in stack format (they finish before they come * back to us). This allows us to do a simple loop to * assign the commit to the tail. */ again: max_count = cpu_buffer->nr_pages * 100; while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) { if (RB_WARN_ON(cpu_buffer, !(--max_count))) return; if (RB_WARN_ON(cpu_buffer, rb_is_reader_page(cpu_buffer->tail_page))) return; local_set(&cpu_buffer->commit_page->page->commit, rb_page_write(cpu_buffer->commit_page)); rb_inc_page(cpu_buffer, &cpu_buffer->commit_page); /* Only update the write stamp if the page has an event */ if (rb_page_write(cpu_buffer->commit_page)) cpu_buffer->write_stamp = cpu_buffer->commit_page->page->time_stamp; /* add barrier to keep gcc from optimizing too much */ barrier(); } while (rb_commit_index(cpu_buffer) != rb_page_write(cpu_buffer->commit_page)) { local_set(&cpu_buffer->commit_page->page->commit, rb_page_write(cpu_buffer->commit_page)); RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->commit_page->page->commit) & ~RB_WRITE_MASK); barrier(); } /* again, keep gcc from optimizing */ barrier(); /* * If an interrupt came in just after the first while loop * and pushed the tail page forward, we will be left with * a dangling commit that will never go forward. */ if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page))) goto again; } static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer) { unsigned long commits; if (RB_WARN_ON(cpu_buffer, !local_read(&cpu_buffer->committing))) return; again: commits = local_read(&cpu_buffer->commits); /* synchronize with interrupts */ barrier(); if (local_read(&cpu_buffer->committing) == 1) rb_set_commit_to_write(cpu_buffer); local_dec(&cpu_buffer->committing); /* synchronize with interrupts */ barrier(); /* * Need to account for interrupts coming in between the * updating of the commit page and the clearing of the * committing counter. */ if (unlikely(local_read(&cpu_buffer->commits) != commits) && !local_read(&cpu_buffer->committing)) { local_inc(&cpu_buffer->committing); goto again; } } static inline void rb_event_discard(struct ring_buffer_event *event) { if (extended_time(event)) event = skip_time_extend(event); /* array[0] holds the actual length for the discarded event */ event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE; event->type_len = RINGBUF_TYPE_PADDING; /* time delta must be non zero */ if (!event->time_delta) event->time_delta = 1; } static __always_inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event) { unsigned long addr = (unsigned long)event; unsigned long index; index = rb_event_index(event); addr &= PAGE_MASK; return cpu_buffer->commit_page->page == (void *)addr && rb_commit_index(cpu_buffer) == index; } static __always_inline void rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event) { u64 delta; /* * The event first in the commit queue updates the * time stamp. */ if (rb_event_is_commit(cpu_buffer, event)) { /* * A commit event that is first on a page * updates the write timestamp with the page stamp */ if (!rb_event_index(event)) cpu_buffer->write_stamp = cpu_buffer->commit_page->page->time_stamp; else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) { delta = ring_buffer_event_time_stamp(event); cpu_buffer->write_stamp += delta; } else if (event->type_len == RINGBUF_TYPE_TIME_STAMP) { delta = ring_buffer_event_time_stamp(event); cpu_buffer->write_stamp = delta; } else cpu_buffer->write_stamp += event->time_delta; } } static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event) { local_inc(&cpu_buffer->entries); rb_update_write_stamp(cpu_buffer, event); rb_end_commit(cpu_buffer); } static __always_inline void rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) { bool pagebusy; if (buffer->irq_work.waiters_pending) { buffer->irq_work.waiters_pending = false; /* irq_work_queue() supplies it's own memory barriers */ irq_work_queue(&buffer->irq_work.work); } if (cpu_buffer->irq_work.waiters_pending) { cpu_buffer->irq_work.waiters_pending = false; /* irq_work_queue() supplies it's own memory barriers */ irq_work_queue(&cpu_buffer->irq_work.work); } pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page; if (!pagebusy && cpu_buffer->irq_work.full_waiters_pending) { cpu_buffer->irq_work.wakeup_full = true; cpu_buffer->irq_work.full_waiters_pending = false; /* irq_work_queue() supplies it's own memory barriers */ irq_work_queue(&cpu_buffer->irq_work.work); } } /* * The lock and unlock are done within a preempt disable section. * The current_context per_cpu variable can only be modified * by the current task between lock and unlock. But it can * be modified more than once via an interrupt. To pass this * information from the lock to the unlock without having to * access the 'in_interrupt()' functions again (which do show * a bit of overhead in something as critical as function tracing, * we use a bitmask trick. * * bit 0 = NMI context * bit 1 = IRQ context * bit 2 = SoftIRQ context * bit 3 = normal context. * * This works because this is the order of contexts that can * preempt other contexts. A SoftIRQ never preempts an IRQ * context. * * When the context is determined, the corresponding bit is * checked and set (if it was set, then a recursion of that context * happened). * * On unlock, we need to clear this bit. To do so, just subtract * 1 from the current_context and AND it to itself. * * (binary) * 101 - 1 = 100 * 101 & 100 = 100 (clearing bit zero) * * 1010 - 1 = 1001 * 1010 & 1001 = 1000 (clearing bit 1) * * The least significant bit can be cleared this way, and it * just so happens that it is the same bit corresponding to * the current context. */ static __always_inline int trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer) { unsigned int val = cpu_buffer->current_context; unsigned long pc = preempt_count(); int bit; if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET))) bit = RB_CTX_NORMAL; else bit = pc & NMI_MASK ? RB_CTX_NMI : pc & HARDIRQ_MASK ? RB_CTX_IRQ : RB_CTX_SOFTIRQ; if (unlikely(val & (1 << (bit + cpu_buffer->nest)))) return 1; val |= (1 << (bit + cpu_buffer->nest)); cpu_buffer->current_context = val; return 0; } static __always_inline void trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer) { cpu_buffer->current_context &= cpu_buffer->current_context - (1 << cpu_buffer->nest); } /* The recursive locking above uses 4 bits */ #define NESTED_BITS 4 /** * ring_buffer_nest_start - Allow to trace while nested * @buffer: The ring buffer to modify * * The ring buffer has a safety mechanism to prevent recursion. * But there may be a case where a trace needs to be done while * tracing something else. In this case, calling this function * will allow this function to nest within a currently active * ring_buffer_lock_reserve(). * * Call this function before calling another ring_buffer_lock_reserve() and * call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit(). */ void ring_buffer_nest_start(struct ring_buffer *buffer) { struct ring_buffer_per_cpu *cpu_buffer; int cpu; /* Enabled by ring_buffer_nest_end() */ preempt_disable_notrace(); cpu = raw_smp_processor_id(); cpu_buffer = buffer->buffers[cpu]; /* This is the shift value for the above recursive locking */ cpu_buffer->nest += NESTED_BITS; } /** * ring_buffer_nest_end - Allow to trace while nested * @buffer: The ring buffer to modify * * Must be called after ring_buffer_nest_start() and after the * ring_buffer_unlock_commit(). */ void ring_buffer_nest_end(struct ring_buffer *buffer) { struct ring_buffer_per_cpu *cpu_buffer; int cpu; /* disabled by ring_buffer_nest_start() */ cpu = raw_smp_processor_id(); cpu_buffer = buffer->buffers[cpu]; /* This is the shift value for the above recursive locking */ cpu_buffer->nest -= NESTED_BITS; preempt_enable_notrace(); } /** * ring_buffer_unlock_commit - commit a reserved * @buffer: The buffer to commit to * @event: The event pointer to commit. * * This commits the data to the ring buffer, and releases any locks held. * * Must be paired with ring_buffer_lock_reserve. */ int ring_buffer_unlock_commit(struct ring_buffer *buffer, struct ring_buffer_event *event) { struct ring_buffer_per_cpu *cpu_buffer; int cpu = raw_smp_processor_id(); cpu_buffer = buffer->buffers[cpu]; rb_commit(cpu_buffer, event); rb_wakeups(buffer, cpu_buffer); trace_recursive_unlock(cpu_buffer); preempt_enable_notrace(); return 0; } EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit); static noinline void rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer, struct rb_event_info *info) { WARN_ONCE(info->delta > (1ULL << 59), KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s", (unsigned long long)info->delta, (unsigned long long)info->ts, (unsigned long long)cpu_buffer->write_stamp, sched_clock_stable() ? "" : "If you just came from a suspend/resume,\n" "please switch to the trace global clock:\n" " echo global > /sys/kernel/debug/tracing/trace_clock\n" "or add trace_clock=global to the kernel command line\n"); info->add_timestamp = 1; } static struct ring_buffer_event * __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer, struct rb_event_info *info) { struct ring_buffer_event *event; struct buffer_page *tail_page; unsigned long tail, write; /* * If the time delta since the last event is too big to * hold in the time field of the event, then we append a * TIME EXTEND event ahead of the data event. */ if (unlikely(info->add_timestamp)) info->length += RB_LEN_TIME_EXTEND; /* Don't let the compiler play games with cpu_buffer->tail_page */ tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page); write = local_add_return(info->length, &tail_page->write); /* set write to only the index of the write */ write &= RB_WRITE_MASK; tail = write - info->length; /* * If this is the first commit on the page, then it has the same * timestamp as the page itself. */ if (!tail && !ring_buffer_time_stamp_abs(cpu_buffer->buffer)) info->delta = 0; /* See if we shot pass the end of this buffer page */ if (unlikely(write > BUF_PAGE_SIZE)) return rb_move_tail(cpu_buffer, tail, info); /* We reserved something on the buffer */ event = __rb_page_index(tail_page, tail); rb_update_event(cpu_buffer, event, info); local_inc(&tail_page->entries); /* * If this is the first commit on the page, then update * its timestamp. */ if (!tail) tail_page->page->time_stamp = info->ts; /* account for these added bytes */ local_add(info->length, &cpu_buffer->entries_bytes); return event; } static __always_inline struct ring_buffer_event * rb_reserve_next_event(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer, unsigned long length) { struct ring_buffer_event *event; struct rb_event_info info; int nr_loops = 0; u64 diff; rb_start_commit(cpu_buffer); #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP /* * Due to the ability to swap a cpu buffer from a buffer * it is possible it was swapped before we committed. * (committing stops a swap). We check for it here and * if it happened, we have to fail the write. */ barrier(); if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) { local_dec(&cpu_buffer->committing); local_dec(&cpu_buffer->commits); return NULL; } #endif info.length = rb_calculate_event_length(length); again: info.add_timestamp = 0; info.delta = 0; /* * We allow for interrupts to reenter here and do a trace. * If one does, it will cause this original code to loop * back here. Even with heavy interrupts happening, this * should only happen a few times in a row. If this happens * 1000 times in a row, there must be either an interrupt * storm or we have something buggy. * Bail! */ if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000)) goto out_fail; info.ts = rb_time_stamp(cpu_buffer->buffer); diff = info.ts - cpu_buffer->write_stamp; /* make sure this diff is calculated here */ barrier(); if (ring_buffer_time_stamp_abs(buffer)) { info.delta = info.ts; rb_handle_timestamp(cpu_buffer, &info); } else /* Did the write stamp get updated already? */ if (likely(info.ts >= cpu_buffer->write_stamp)) { info.delta = diff; if (unlikely(test_time_stamp(info.delta))) rb_handle_timestamp(cpu_buffer, &info); } event = __rb_reserve_next(cpu_buffer, &info); if (unlikely(PTR_ERR(event) == -EAGAIN)) { if (info.add_timestamp) info.length -= RB_LEN_TIME_EXTEND; goto again; } if (!event) goto out_fail; return event; out_fail: rb_end_commit(cpu_buffer); return NULL; } /** * ring_buffer_lock_reserve - reserve a part of the buffer * @buffer: the ring buffer to reserve from * @length: the length of the data to reserve (excluding event header) * * Returns a reserved event on the ring buffer to copy directly to. * The user of this interface will need to get the body to write into * and can use the ring_buffer_event_data() interface. * * The length is the length of the data needed, not the event length * which also includes the event header. * * Must be paired with ring_buffer_unlock_commit, unless NULL is returned. * If NULL is returned, then nothing has been allocated or locked. */ struct ring_buffer_event * ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length) { struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_event *event; int cpu; /* If we are tracing schedule, we don't want to recurse */ preempt_disable_notrace(); if (unlikely(atomic_read(&buffer->record_disabled))) goto out; cpu = raw_smp_processor_id(); if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask))) goto out; cpu_buffer = buffer->buffers[cpu]; if (unlikely(atomic_read(&cpu_buffer->record_disabled))) goto out; if (unlikely(length > BUF_MAX_DATA_SIZE)) goto out; if (unlikely(trace_recursive_lock(cpu_buffer))) goto out; event = rb_reserve_next_event(buffer, cpu_buffer, length); if (!event) goto out_unlock; return event; out_unlock: trace_recursive_unlock(cpu_buffer); out: preempt_enable_notrace(); return NULL; } EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve); /* * Decrement the entries to the page that an event is on. * The event does not even need to exist, only the pointer * to the page it is on. This may only be called before the commit * takes place. */ static inline void rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event) { unsigned long addr = (unsigned long)event; struct buffer_page *bpage = cpu_buffer->commit_page; struct buffer_page *start; addr &= PAGE_MASK; /* Do the likely case first */ if (likely(bpage->page == (void *)addr)) { local_dec(&bpage->entries); return; } /* * Because the commit page may be on the reader page we * start with the next page and check the end loop there. */ rb_inc_page(cpu_buffer, &bpage); start = bpage; do { if (bpage->page == (void *)addr) { local_dec(&bpage->entries); return; } rb_inc_page(cpu_buffer, &bpage); } while (bpage != start); /* commit not part of this buffer?? */ RB_WARN_ON(cpu_buffer, 1); } /** * ring_buffer_commit_discard - discard an event that has not been committed * @buffer: the ring buffer * @event: non committed event to discard * * Sometimes an event that is in the ring buffer needs to be ignored. * This function lets the user discard an event in the ring buffer * and then that event will not be read later. * * This function only works if it is called before the item has been * committed. It will try to free the event from the ring buffer * if another event has not been added behind it. * * If another event has been added behind it, it will set the event * up as discarded, and perform the commit. * * If this function is called, do not call ring_buffer_unlock_commit on * the event. */ void ring_buffer_discard_commit(struct ring_buffer *buffer, struct ring_buffer_event *event) { struct ring_buffer_per_cpu *cpu_buffer; int cpu; /* The event is discarded regardless */ rb_event_discard(event); cpu = smp_processor_id(); cpu_buffer = buffer->buffers[cpu]; /* * This must only be called if the event has not been * committed yet. Thus we can assume that preemption * is still disabled. */ RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing)); rb_decrement_entry(cpu_buffer, event); if (rb_try_to_discard(cpu_buffer, event)) goto out; /* * The commit is still visible by the reader, so we * must still update the timestamp. */ rb_update_write_stamp(cpu_buffer, event); out: rb_end_commit(cpu_buffer); trace_recursive_unlock(cpu_buffer); preempt_enable_notrace(); } EXPORT_SYMBOL_GPL(ring_buffer_discard_commit); /** * ring_buffer_write - write data to the buffer without reserving * @buffer: The ring buffer to write to. * @length: The length of the data being written (excluding the event header) * @data: The data to write to the buffer. * * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as * one function. If you already have the data to write to the buffer, it * may be easier to simply call this function. * * Note, like ring_buffer_lock_reserve, the length is the length of the data * and not the length of the event which would hold the header. */ int ring_buffer_write(struct ring_buffer *buffer, unsigned long length, void *data) { struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_event *event; void *body; int ret = -EBUSY; int cpu; preempt_disable_notrace(); if (atomic_read(&buffer->record_disabled)) goto out; cpu = raw_smp_processor_id(); if (!cpumask_test_cpu(cpu, buffer->cpumask)) goto out; cpu_buffer = buffer->buffers[cpu]; if (atomic_read(&cpu_buffer->record_disabled)) goto out; if (length > BUF_MAX_DATA_SIZE) goto out; if (unlikely(trace_recursive_lock(cpu_buffer))) goto out; event = rb_reserve_next_event(buffer, cpu_buffer, length); if (!event) goto out_unlock; body = rb_event_data(event); memcpy(body, data, length); rb_commit(cpu_buffer, event); rb_wakeups(buffer, cpu_buffer); ret = 0; out_unlock: trace_recursive_unlock(cpu_buffer); out: preempt_enable_notrace(); return ret; } EXPORT_SYMBOL_GPL(ring_buffer_write); static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer) { struct buffer_page *reader = cpu_buffer->reader_page; struct buffer_page *head = rb_set_head_page(cpu_buffer); struct buffer_page *commit = cpu_buffer->commit_page; /* In case of error, head will be NULL */ if (unlikely(!head)) return true; return reader->read == rb_page_commit(reader) && (commit == reader || (commit == head && head->read == rb_page_commit(commit))); } /** * ring_buffer_record_disable - stop all writes into the buffer * @buffer: The ring buffer to stop writes to. * * This prevents all writes to the buffer. Any attempt to write * to the buffer after this will fail and return NULL. * * The caller should call synchronize_sched() after this. */ void ring_buffer_record_disable(struct ring_buffer *buffer) { atomic_inc(&buffer->record_disabled); } EXPORT_SYMBOL_GPL(ring_buffer_record_disable); /** * ring_buffer_record_enable - enable writes to the buffer * @buffer: The ring buffer to enable writes * * Note, multiple disables will need the same number of enables * to truly enable the writing (much like preempt_disable). */ void ring_buffer_record_enable(struct ring_buffer *buffer) { atomic_dec(&buffer->record_disabled); } EXPORT_SYMBOL_GPL(ring_buffer_record_enable); /** * ring_buffer_record_off - stop all writes into the buffer * @buffer: The ring buffer to stop writes to. * * This prevents all writes to the buffer. Any attempt to write * to the buffer after this will fail and return NULL. * * This is different than ring_buffer_record_disable() as * it works like an on/off switch, where as the disable() version * must be paired with a enable(). */ void ring_buffer_record_off(struct ring_buffer *buffer) { unsigned int rd; unsigned int new_rd; do { rd = atomic_read(&buffer->record_disabled); new_rd = rd | RB_BUFFER_OFF; } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd); } EXPORT_SYMBOL_GPL(ring_buffer_record_off); /** * ring_buffer_record_on - restart writes into the buffer * @buffer: The ring buffer to start writes to. * * This enables all writes to the buffer that was disabled by * ring_buffer_record_off(). * * This is different than ring_buffer_record_enable() as * it works like an on/off switch, where as the enable() version * must be paired with a disable(). */ void ring_buffer_record_on(struct ring_buffer *buffer) { unsigned int rd; unsigned int new_rd; do { rd = atomic_read(&buffer->record_disabled); new_rd = rd & ~RB_BUFFER_OFF; } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd); } EXPORT_SYMBOL_GPL(ring_buffer_record_on); /** * ring_buffer_record_is_on - return true if the ring buffer can write * @buffer: The ring buffer to see if write is enabled * * Returns true if the ring buffer is in a state that it accepts writes. */ bool ring_buffer_record_is_on(struct ring_buffer *buffer) { return !atomic_read(&buffer->record_disabled); } /** * ring_buffer_record_is_set_on - return true if the ring buffer is set writable * @buffer: The ring buffer to see if write is set enabled * * Returns true if the ring buffer is set writable by ring_buffer_record_on(). * Note that this does NOT mean it is in a writable state. * * It may return true when the ring buffer has been disabled by * ring_buffer_record_disable(), as that is a temporary disabling of * the ring buffer. */ bool ring_buffer_record_is_set_on(struct ring_buffer *buffer) { return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF); } /** * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer * @buffer: The ring buffer to stop writes to. * @cpu: The CPU buffer to stop * * This prevents all writes to the buffer. Any attempt to write * to the buffer after this will fail and return NULL. * * The caller should call synchronize_sched() after this. */ void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return; cpu_buffer = buffer->buffers[cpu]; atomic_inc(&cpu_buffer->record_disabled); } EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu); /** * ring_buffer_record_enable_cpu - enable writes to the buffer * @buffer: The ring buffer to enable writes * @cpu: The CPU to enable. * * Note, multiple disables will need the same number of enables * to truly enable the writing (much like preempt_disable). */ void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return; cpu_buffer = buffer->buffers[cpu]; atomic_dec(&cpu_buffer->record_disabled); } EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu); /* * The total entries in the ring buffer is the running counter * of entries entered into the ring buffer, minus the sum of * the entries read from the ring buffer and the number of * entries that were overwritten. */ static inline unsigned long rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer) { return local_read(&cpu_buffer->entries) - (local_read(&cpu_buffer->overrun) + cpu_buffer->read); } /** * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer * @buffer: The ring buffer * @cpu: The per CPU buffer to read from. */ u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu) { unsigned long flags; struct ring_buffer_per_cpu *cpu_buffer; struct buffer_page *bpage; u64 ret = 0; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; cpu_buffer = buffer->buffers[cpu]; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); /* * if the tail is on reader_page, oldest time stamp is on the reader * page */ if (cpu_buffer->tail_page == cpu_buffer->reader_page) bpage = cpu_buffer->reader_page; else bpage = rb_set_head_page(cpu_buffer); if (bpage) ret = bpage->page->time_stamp; raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); return ret; } EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts); /** * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer * @buffer: The ring buffer * @cpu: The per CPU buffer to read from. */ unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long ret; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; cpu_buffer = buffer->buffers[cpu]; ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes; return ret; } EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu); /** * ring_buffer_entries_cpu - get the number of entries in a cpu buffer * @buffer: The ring buffer * @cpu: The per CPU buffer to get the entries from. */ unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; cpu_buffer = buffer->buffers[cpu]; return rb_num_of_entries(cpu_buffer); } EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu); /** * ring_buffer_overrun_cpu - get the number of overruns caused by the ring * buffer wrapping around (only if RB_FL_OVERWRITE is on). * @buffer: The ring buffer * @cpu: The per CPU buffer to get the number of overruns from */ unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long ret; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; cpu_buffer = buffer->buffers[cpu]; ret = local_read(&cpu_buffer->overrun); return ret; } EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu); /** * ring_buffer_commit_overrun_cpu - get the number of overruns caused by * commits failing due to the buffer wrapping around while there are uncommitted * events, such as during an interrupt storm. * @buffer: The ring buffer * @cpu: The per CPU buffer to get the number of overruns from */ unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long ret; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; cpu_buffer = buffer->buffers[cpu]; ret = local_read(&cpu_buffer->commit_overrun); return ret; } EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu); /** * ring_buffer_dropped_events_cpu - get the number of dropped events caused by * the ring buffer filling up (only if RB_FL_OVERWRITE is off). * @buffer: The ring buffer * @cpu: The per CPU buffer to get the number of overruns from */ unsigned long ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long ret; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; cpu_buffer = buffer->buffers[cpu]; ret = local_read(&cpu_buffer->dropped_events); return ret; } EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu); /** * ring_buffer_read_events_cpu - get the number of events successfully read * @buffer: The ring buffer * @cpu: The per CPU buffer to get the number of events read */ unsigned long ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; cpu_buffer = buffer->buffers[cpu]; return cpu_buffer->read; } EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu); /** * ring_buffer_entries - get the number of entries in a buffer * @buffer: The ring buffer * * Returns the total number of entries in the ring buffer * (all CPU entries) */ unsigned long ring_buffer_entries(struct ring_buffer *buffer) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long entries = 0; int cpu; /* if you care about this being correct, lock the buffer */ for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu]; entries += rb_num_of_entries(cpu_buffer); } return entries; } EXPORT_SYMBOL_GPL(ring_buffer_entries); /** * ring_buffer_overruns - get the number of overruns in buffer * @buffer: The ring buffer * * Returns the total number of overruns in the ring buffer * (all CPU entries) */ unsigned long ring_buffer_overruns(struct ring_buffer *buffer) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long overruns = 0; int cpu; /* if you care about this being correct, lock the buffer */ for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu]; overruns += local_read(&cpu_buffer->overrun); } return overruns; } EXPORT_SYMBOL_GPL(ring_buffer_overruns); static void rb_iter_reset(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; /* Iterator usage is expected to have record disabled */ iter->head_page = cpu_buffer->reader_page; iter->head = cpu_buffer->reader_page->read; iter->cache_reader_page = iter->head_page; iter->cache_read = cpu_buffer->read; if (iter->head) iter->read_stamp = cpu_buffer->read_stamp; else iter->read_stamp = iter->head_page->page->time_stamp; } /** * ring_buffer_iter_reset - reset an iterator * @iter: The iterator to reset * * Resets the iterator, so that it will start from the beginning * again. */ void ring_buffer_iter_reset(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long flags; if (!iter) return; cpu_buffer = iter->cpu_buffer; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); rb_iter_reset(iter); raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); } EXPORT_SYMBOL_GPL(ring_buffer_iter_reset); /** * ring_buffer_iter_empty - check if an iterator has no more to read * @iter: The iterator to check */ int ring_buffer_iter_empty(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer; struct buffer_page *reader; struct buffer_page *head_page; struct buffer_page *commit_page; unsigned commit; cpu_buffer = iter->cpu_buffer; /* Remember, trace recording is off when iterator is in use */ reader = cpu_buffer->reader_page; head_page = cpu_buffer->head_page; commit_page = cpu_buffer->commit_page; commit = rb_page_commit(commit_page); return ((iter->head_page == commit_page && iter->head == commit) || (iter->head_page == reader && commit_page == head_page && head_page->read == commit && iter->head == rb_page_commit(cpu_buffer->reader_page))); } EXPORT_SYMBOL_GPL(ring_buffer_iter_empty); static void rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_event *event) { u64 delta; switch (event->type_len) { case RINGBUF_TYPE_PADDING: return; case RINGBUF_TYPE_TIME_EXTEND: delta = ring_buffer_event_time_stamp(event); cpu_buffer->read_stamp += delta; return; case RINGBUF_TYPE_TIME_STAMP: delta = ring_buffer_event_time_stamp(event); cpu_buffer->read_stamp = delta; return; case RINGBUF_TYPE_DATA: cpu_buffer->read_stamp += event->time_delta; return; default: BUG(); } return; } static void rb_update_iter_read_stamp(struct ring_buffer_iter *iter, struct ring_buffer_event *event) { u64 delta; switch (event->type_len) { case RINGBUF_TYPE_PADDING: return; case RINGBUF_TYPE_TIME_EXTEND: delta = ring_buffer_event_time_stamp(event); iter->read_stamp += delta; return; case RINGBUF_TYPE_TIME_STAMP: delta = ring_buffer_event_time_stamp(event); iter->read_stamp = delta; return; case RINGBUF_TYPE_DATA: iter->read_stamp += event->time_delta; return; default: BUG(); } return; } static struct buffer_page * rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) { struct buffer_page *reader = NULL; unsigned long overwrite; unsigned long flags; int nr_loops = 0; int ret; local_irq_save(flags); arch_spin_lock(&cpu_buffer->lock); again: /* * This should normally only loop twice. But because the * start of the reader inserts an empty page, it causes * a case where we will loop three times. There should be no * reason to loop four times (that I know of). */ if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) { reader = NULL; goto out; } reader = cpu_buffer->reader_page; /* If there's more to read, return this page */ if (cpu_buffer->reader_page->read < rb_page_size(reader)) goto out; /* Never should we have an index greater than the size */ if (RB_WARN_ON(cpu_buffer, cpu_buffer->reader_page->read > rb_page_size(reader))) goto out; /* check if we caught up to the tail */ reader = NULL; if (cpu_buffer->commit_page == cpu_buffer->reader_page) goto out; /* Don't bother swapping if the ring buffer is empty */ if (rb_num_of_entries(cpu_buffer) == 0) goto out; /* * Reset the reader page to size zero. */ local_set(&cpu_buffer->reader_page->write, 0); local_set(&cpu_buffer->reader_page->entries, 0); local_set(&cpu_buffer->reader_page->page->commit, 0); cpu_buffer->reader_page->real_end = 0; spin: /* * Splice the empty reader page into the list around the head. */ reader = rb_set_head_page(cpu_buffer); if (!reader) goto out; cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next); cpu_buffer->reader_page->list.prev = reader->list.prev; /* * cpu_buffer->pages just needs to point to the buffer, it * has no specific buffer page to point to. Lets move it out * of our way so we don't accidentally swap it. */ cpu_buffer->pages = reader->list.prev; /* The reader page will be pointing to the new head */ rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list); /* * We want to make sure we read the overruns after we set up our * pointers to the next object. The writer side does a * cmpxchg to cross pages which acts as the mb on the writer * side. Note, the reader will constantly fail the swap * while the writer is updating the pointers, so this * guarantees that the overwrite recorded here is the one we * want to compare with the last_overrun. */ smp_mb(); overwrite = local_read(&(cpu_buffer->overrun)); /* * Here's the tricky part. * * We need to move the pointer past the header page. * But we can only do that if a writer is not currently * moving it. The page before the header page has the * flag bit '1' set if it is pointing to the page we want. * but if the writer is in the process of moving it * than it will be '2' or already moved '0'. */ ret = rb_head_page_replace(reader, cpu_buffer->reader_page); /* * If we did not convert it, then we must try again. */ if (!ret) goto spin; /* * Yeah! We succeeded in replacing the page. * * Now make the new head point back to the reader page. */ rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list; rb_inc_page(cpu_buffer, &cpu_buffer->head_page); /* Finally update the reader page to the new head */ cpu_buffer->reader_page = reader; cpu_buffer->reader_page->read = 0; if (overwrite != cpu_buffer->last_overrun) { cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun; cpu_buffer->last_overrun = overwrite; } goto again; out: /* Update the read_stamp on the first event */ if (reader && reader->read == 0) cpu_buffer->read_stamp = reader->page->time_stamp; arch_spin_unlock(&cpu_buffer->lock); local_irq_restore(flags); return reader; } static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer) { struct ring_buffer_event *event; struct buffer_page *reader; unsigned length; reader = rb_get_reader_page(cpu_buffer); /* This function should not be called when buffer is empty */ if (RB_WARN_ON(cpu_buffer, !reader)) return; event = rb_reader_event(cpu_buffer); if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX) cpu_buffer->read++; rb_update_read_stamp(cpu_buffer, event); length = rb_event_length(event); cpu_buffer->reader_page->read += length; } static void rb_advance_iter(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_event *event; unsigned length; cpu_buffer = iter->cpu_buffer; /* * Check if we are at the end of the buffer. */ if (iter->head >= rb_page_size(iter->head_page)) { /* discarded commits can make the page empty */ if (iter->head_page == cpu_buffer->commit_page) return; rb_inc_iter(iter); return; } event = rb_iter_head_event(iter); length = rb_event_length(event); /* * This should not be called to advance the header if we are * at the tail of the buffer. */ if (RB_WARN_ON(cpu_buffer, (iter->head_page == cpu_buffer->commit_page) && (iter->head + length > rb_commit_index(cpu_buffer)))) return; rb_update_iter_read_stamp(iter, event); iter->head += length; /* check for end of page padding */ if ((iter->head >= rb_page_size(iter->head_page)) && (iter->head_page != cpu_buffer->commit_page)) rb_inc_iter(iter); } static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer) { return cpu_buffer->lost_events; } static struct ring_buffer_event * rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts, unsigned long *lost_events) { struct ring_buffer_event *event; struct buffer_page *reader; int nr_loops = 0; if (ts) *ts = 0; again: /* * We repeat when a time extend is encountered. * Since the time extend is always attached to a data event, * we should never loop more than once. * (We never hit the following condition more than twice). */ if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2)) return NULL; reader = rb_get_reader_page(cpu_buffer); if (!reader) return NULL; event = rb_reader_event(cpu_buffer); switch (event->type_len) { case RINGBUF_TYPE_PADDING: if (rb_null_event(event)) RB_WARN_ON(cpu_buffer, 1); /* * Because the writer could be discarding every * event it creates (which would probably be bad) * if we were to go back to "again" then we may never * catch up, and will trigger the warn on, or lock * the box. Return the padding, and we will release * the current locks, and try again. */ return event; case RINGBUF_TYPE_TIME_EXTEND: /* Internal data, OK to advance */ rb_advance_reader(cpu_buffer); goto again; case RINGBUF_TYPE_TIME_STAMP: if (ts) { *ts = ring_buffer_event_time_stamp(event); ring_buffer_normalize_time_stamp(cpu_buffer->buffer, cpu_buffer->cpu, ts); } /* Internal data, OK to advance */ rb_advance_reader(cpu_buffer); goto again; case RINGBUF_TYPE_DATA: if (ts && !(*ts)) { *ts = cpu_buffer->read_stamp + event->time_delta; ring_buffer_normalize_time_stamp(cpu_buffer->buffer, cpu_buffer->cpu, ts); } if (lost_events) *lost_events = rb_lost_events(cpu_buffer); return event; default: BUG(); } return NULL; } EXPORT_SYMBOL_GPL(ring_buffer_peek); static struct ring_buffer_event * rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts) { struct ring_buffer *buffer; struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_event *event; int nr_loops = 0; if (ts) *ts = 0; cpu_buffer = iter->cpu_buffer; buffer = cpu_buffer->buffer; /* * Check if someone performed a consuming read to * the buffer. A consuming read invalidates the iterator * and we need to reset the iterator in this case. */ if (unlikely(iter->cache_read != cpu_buffer->read || iter->cache_reader_page != cpu_buffer->reader_page)) rb_iter_reset(iter); again: if (ring_buffer_iter_empty(iter)) return NULL; /* * We repeat when a time extend is encountered or we hit * the end of the page. Since the time extend is always attached * to a data event, we should never loop more than three times. * Once for going to next page, once on time extend, and * finally once to get the event. * (We never hit the following condition more than thrice). */ if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) return NULL; if (rb_per_cpu_empty(cpu_buffer)) return NULL; if (iter->head >= rb_page_size(iter->head_page)) { rb_inc_iter(iter); goto again; } event = rb_iter_head_event(iter); switch (event->type_len) { case RINGBUF_TYPE_PADDING: if (rb_null_event(event)) { rb_inc_iter(iter); goto again; } rb_advance_iter(iter); return event; case RINGBUF_TYPE_TIME_EXTEND: /* Internal data, OK to advance */ rb_advance_iter(iter); goto again; case RINGBUF_TYPE_TIME_STAMP: if (ts) { *ts = ring_buffer_event_time_stamp(event); ring_buffer_normalize_time_stamp(cpu_buffer->buffer, cpu_buffer->cpu, ts); } /* Internal data, OK to advance */ rb_advance_iter(iter); goto again; case RINGBUF_TYPE_DATA: if (ts && !(*ts)) { *ts = iter->read_stamp + event->time_delta; ring_buffer_normalize_time_stamp(buffer, cpu_buffer->cpu, ts); } return event; default: BUG(); } return NULL; } EXPORT_SYMBOL_GPL(ring_buffer_iter_peek); static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer) { if (likely(!in_nmi())) { raw_spin_lock(&cpu_buffer->reader_lock); return true; } /* * If an NMI die dumps out the content of the ring buffer * trylock must be used to prevent a deadlock if the NMI * preempted a task that holds the ring buffer locks. If * we get the lock then all is fine, if not, then continue * to do the read, but this can corrupt the ring buffer, * so it must be permanently disabled from future writes. * Reading from NMI is a oneshot deal. */ if (raw_spin_trylock(&cpu_buffer->reader_lock)) return true; /* Continue without locking, but disable the ring buffer */ atomic_inc(&cpu_buffer->record_disabled); return false; } static inline void rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked) { if (likely(locked)) raw_spin_unlock(&cpu_buffer->reader_lock); return; } /** * ring_buffer_peek - peek at the next event to be read * @buffer: The ring buffer to read * @cpu: The cpu to peak at * @ts: The timestamp counter of this event. * @lost_events: a variable to store if events were lost (may be NULL) * * This will return the event that will be read next, but does * not consume the data. */ struct ring_buffer_event * ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts, unsigned long *lost_events) { struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu]; struct ring_buffer_event *event; unsigned long flags; bool dolock; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return NULL; again: local_irq_save(flags); dolock = rb_reader_lock(cpu_buffer); event = rb_buffer_peek(cpu_buffer, ts, lost_events); if (event && event->type_len == RINGBUF_TYPE_PADDING) rb_advance_reader(cpu_buffer); rb_reader_unlock(cpu_buffer, dolock); local_irq_restore(flags); if (event && event->type_len == RINGBUF_TYPE_PADDING) goto again; return event; } /** * ring_buffer_iter_peek - peek at the next event to be read * @iter: The ring buffer iterator * @ts: The timestamp counter of this event. * * This will return the event that will be read next, but does * not increment the iterator. */ struct ring_buffer_event * ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts) { struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; struct ring_buffer_event *event; unsigned long flags; again: raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); event = rb_iter_peek(iter, ts); raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); if (event && event->type_len == RINGBUF_TYPE_PADDING) goto again; return event; } /** * ring_buffer_consume - return an event and consume it * @buffer: The ring buffer to get the next event from * @cpu: the cpu to read the buffer from * @ts: a variable to store the timestamp (may be NULL) * @lost_events: a variable to store if events were lost (may be NULL) * * Returns the next event in the ring buffer, and that event is consumed. * Meaning, that sequential reads will keep returning a different event, * and eventually empty the ring buffer if the producer is slower. */ struct ring_buffer_event * ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts, unsigned long *lost_events) { struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_event *event = NULL; unsigned long flags; bool dolock; again: /* might be called in atomic */ preempt_disable(); if (!cpumask_test_cpu(cpu, buffer->cpumask)) goto out; cpu_buffer = buffer->buffers[cpu]; local_irq_save(flags); dolock = rb_reader_lock(cpu_buffer); event = rb_buffer_peek(cpu_buffer, ts, lost_events); if (event) { cpu_buffer->lost_events = 0; rb_advance_reader(cpu_buffer); } rb_reader_unlock(cpu_buffer, dolock); local_irq_restore(flags); out: preempt_enable(); if (event && event->type_len == RINGBUF_TYPE_PADDING) goto again; return event; } EXPORT_SYMBOL_GPL(ring_buffer_consume); /** * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer * @buffer: The ring buffer to read from * @cpu: The cpu buffer to iterate over * * This performs the initial preparations necessary to iterate * through the buffer. Memory is allocated, buffer recording * is disabled, and the iterator pointer is returned to the caller. * * Disabling buffer recording prevents the reading from being * corrupted. This is not a consuming read, so a producer is not * expected. * * After a sequence of ring_buffer_read_prepare calls, the user is * expected to make at least one call to ring_buffer_read_prepare_sync. * Afterwards, ring_buffer_read_start is invoked to get things going * for real. * * This overall must be paired with ring_buffer_read_finish. */ struct ring_buffer_iter * ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_iter *iter; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return NULL; iter = kmalloc(sizeof(*iter), GFP_KERNEL); if (!iter) return NULL; cpu_buffer = buffer->buffers[cpu]; iter->cpu_buffer = cpu_buffer; atomic_inc(&buffer->resize_disabled); atomic_inc(&cpu_buffer->record_disabled); return iter; } EXPORT_SYMBOL_GPL(ring_buffer_read_prepare); /** * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls * * All previously invoked ring_buffer_read_prepare calls to prepare * iterators will be synchronized. Afterwards, read_buffer_read_start * calls on those iterators are allowed. */ void ring_buffer_read_prepare_sync(void) { synchronize_sched(); } EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync); /** * ring_buffer_read_start - start a non consuming read of the buffer * @iter: The iterator returned by ring_buffer_read_prepare * * This finalizes the startup of an iteration through the buffer. * The iterator comes from a call to ring_buffer_read_prepare and * an intervening ring_buffer_read_prepare_sync must have been * performed. * * Must be paired with ring_buffer_read_finish. */ void ring_buffer_read_start(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long flags; if (!iter) return; cpu_buffer = iter->cpu_buffer; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); arch_spin_lock(&cpu_buffer->lock); rb_iter_reset(iter); arch_spin_unlock(&cpu_buffer->lock); raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); } EXPORT_SYMBOL_GPL(ring_buffer_read_start); /** * ring_buffer_read_finish - finish reading the iterator of the buffer * @iter: The iterator retrieved by ring_buffer_start * * This re-enables the recording to the buffer, and frees the * iterator. */ void ring_buffer_read_finish(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; unsigned long flags; /* * Ring buffer is disabled from recording, here's a good place * to check the integrity of the ring buffer. * Must prevent readers from trying to read, as the check * clears the HEAD page and readers require it. */ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); rb_check_pages(cpu_buffer); raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); atomic_dec(&cpu_buffer->record_disabled); atomic_dec(&cpu_buffer->buffer->resize_disabled); kfree(iter); } EXPORT_SYMBOL_GPL(ring_buffer_read_finish); /** * ring_buffer_read - read the next item in the ring buffer by the iterator * @iter: The ring buffer iterator * @ts: The time stamp of the event read. * * This reads the next event in the ring buffer and increments the iterator. */ struct ring_buffer_event * ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts) { struct ring_buffer_event *event; struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; unsigned long flags; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); again: event = rb_iter_peek(iter, ts); if (!event) goto out; if (event->type_len == RINGBUF_TYPE_PADDING) goto again; rb_advance_iter(iter); out: raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); return event; } EXPORT_SYMBOL_GPL(ring_buffer_read); /** * ring_buffer_size - return the size of the ring buffer (in bytes) * @buffer: The ring buffer. */ unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu) { /* * Earlier, this method returned * BUF_PAGE_SIZE * buffer->nr_pages * Since the nr_pages field is now removed, we have converted this to * return the per cpu buffer value. */ if (!cpumask_test_cpu(cpu, buffer->cpumask)) return 0; return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages; } EXPORT_SYMBOL_GPL(ring_buffer_size); static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { rb_head_page_deactivate(cpu_buffer); cpu_buffer->head_page = list_entry(cpu_buffer->pages, struct buffer_page, list); local_set(&cpu_buffer->head_page->write, 0); local_set(&cpu_buffer->head_page->entries, 0); local_set(&cpu_buffer->head_page->page->commit, 0); cpu_buffer->head_page->read = 0; cpu_buffer->tail_page = cpu_buffer->head_page; cpu_buffer->commit_page = cpu_buffer->head_page; INIT_LIST_HEAD(&cpu_buffer->reader_page->list); INIT_LIST_HEAD(&cpu_buffer->new_pages); local_set(&cpu_buffer->reader_page->write, 0); local_set(&cpu_buffer->reader_page->entries, 0); local_set(&cpu_buffer->reader_page->page->commit, 0); cpu_buffer->reader_page->read = 0; local_set(&cpu_buffer->entries_bytes, 0); local_set(&cpu_buffer->overrun, 0); local_set(&cpu_buffer->commit_overrun, 0); local_set(&cpu_buffer->dropped_events, 0); local_set(&cpu_buffer->entries, 0); local_set(&cpu_buffer->committing, 0); local_set(&cpu_buffer->commits, 0); cpu_buffer->read = 0; cpu_buffer->read_bytes = 0; cpu_buffer->write_stamp = 0; cpu_buffer->read_stamp = 0; cpu_buffer->lost_events = 0; cpu_buffer->last_overrun = 0; rb_head_page_activate(cpu_buffer); } /** * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer * @buffer: The ring buffer to reset a per cpu buffer of * @cpu: The CPU buffer to be reset */ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu]; unsigned long flags; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return; atomic_inc(&buffer->resize_disabled); atomic_inc(&cpu_buffer->record_disabled); /* Make sure all commits have finished */ synchronize_sched(); raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing))) goto out; arch_spin_lock(&cpu_buffer->lock); rb_reset_cpu(cpu_buffer); arch_spin_unlock(&cpu_buffer->lock); out: raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); atomic_dec(&cpu_buffer->record_disabled); atomic_dec(&buffer->resize_disabled); } EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu); /** * ring_buffer_reset - reset a ring buffer * @buffer: The ring buffer to reset all cpu buffers */ void ring_buffer_reset(struct ring_buffer *buffer) { int cpu; for_each_buffer_cpu(buffer, cpu) ring_buffer_reset_cpu(buffer, cpu); } EXPORT_SYMBOL_GPL(ring_buffer_reset); /** * rind_buffer_empty - is the ring buffer empty? * @buffer: The ring buffer to test */ bool ring_buffer_empty(struct ring_buffer *buffer) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long flags; bool dolock; int cpu; int ret; /* yes this is racy, but if you don't like the race, lock the buffer */ for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu]; local_irq_save(flags); dolock = rb_reader_lock(cpu_buffer); ret = rb_per_cpu_empty(cpu_buffer); rb_reader_unlock(cpu_buffer, dolock); local_irq_restore(flags); if (!ret) return false; } return true; } EXPORT_SYMBOL_GPL(ring_buffer_empty); /** * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty? * @buffer: The ring buffer * @cpu: The CPU buffer to test */ bool ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; unsigned long flags; bool dolock; int ret; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return true; cpu_buffer = buffer->buffers[cpu]; local_irq_save(flags); dolock = rb_reader_lock(cpu_buffer); ret = rb_per_cpu_empty(cpu_buffer); rb_reader_unlock(cpu_buffer, dolock); local_irq_restore(flags); return ret; } EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu); #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP /** * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers * @buffer_a: One buffer to swap with * @buffer_b: The other buffer to swap with * * This function is useful for tracers that want to take a "snapshot" * of a CPU buffer and has another back up buffer lying around. * it is expected that the tracer handles the cpu buffer not being * used at the moment. */ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a, struct ring_buffer *buffer_b, int cpu) { struct ring_buffer_per_cpu *cpu_buffer_a; struct ring_buffer_per_cpu *cpu_buffer_b; int ret = -EINVAL; if (!cpumask_test_cpu(cpu, buffer_a->cpumask) || !cpumask_test_cpu(cpu, buffer_b->cpumask)) goto out; cpu_buffer_a = buffer_a->buffers[cpu]; cpu_buffer_b = buffer_b->buffers[cpu]; /* At least make sure the two buffers are somewhat the same */ if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages) goto out; ret = -EAGAIN; if (atomic_read(&buffer_a->record_disabled)) goto out; if (atomic_read(&buffer_b->record_disabled)) goto out; if (atomic_read(&cpu_buffer_a->record_disabled)) goto out; if (atomic_read(&cpu_buffer_b->record_disabled)) goto out; /* * We can't do a synchronize_sched here because this * function can be called in atomic context. * Normally this will be called from the same CPU as cpu. * If not it's up to the caller to protect this. */ atomic_inc(&cpu_buffer_a->record_disabled); atomic_inc(&cpu_buffer_b->record_disabled); ret = -EBUSY; if (local_read(&cpu_buffer_a->committing)) goto out_dec; if (local_read(&cpu_buffer_b->committing)) goto out_dec; buffer_a->buffers[cpu] = cpu_buffer_b; buffer_b->buffers[cpu] = cpu_buffer_a; cpu_buffer_b->buffer = buffer_a; cpu_buffer_a->buffer = buffer_b; ret = 0; out_dec: atomic_dec(&cpu_buffer_a->record_disabled); atomic_dec(&cpu_buffer_b->record_disabled); out: return ret; } EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu); #endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */ /** * ring_buffer_alloc_read_page - allocate a page to read from buffer * @buffer: the buffer to allocate for. * @cpu: the cpu buffer to allocate. * * This function is used in conjunction with ring_buffer_read_page. * When reading a full page from the ring buffer, these functions * can be used to speed up the process. The calling function should * allocate a few pages first with this function. Then when it * needs to get pages from the ring buffer, it passes the result * of this function into ring_buffer_read_page, which will swap * the page that was allocated, with the read page of the buffer. * * Returns: * The page allocated, or ERR_PTR */ void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; struct buffer_data_page *bpage = NULL; unsigned long flags; struct page *page; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return ERR_PTR(-ENODEV); cpu_buffer = buffer->buffers[cpu]; local_irq_save(flags); arch_spin_lock(&cpu_buffer->lock); if (cpu_buffer->free_page) { bpage = cpu_buffer->free_page; cpu_buffer->free_page = NULL; } arch_spin_unlock(&cpu_buffer->lock); local_irq_restore(flags); if (bpage) goto out; page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_NORETRY, 0); if (!page) return ERR_PTR(-ENOMEM); bpage = page_address(page); out: rb_init_page(bpage); return bpage; } EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page); /** * ring_buffer_free_read_page - free an allocated read page * @buffer: the buffer the page was allocate for * @cpu: the cpu buffer the page came from * @data: the page to free * * Free a page allocated from ring_buffer_alloc_read_page. */ void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data) { struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu]; struct buffer_data_page *bpage = data; struct page *page = virt_to_page(bpage); unsigned long flags; /* If the page is still in use someplace else, we can't reuse it */ if (page_ref_count(page) > 1) goto out; local_irq_save(flags); arch_spin_lock(&cpu_buffer->lock); if (!cpu_buffer->free_page) { cpu_buffer->free_page = bpage; bpage = NULL; } arch_spin_unlock(&cpu_buffer->lock); local_irq_restore(flags); out: free_page((unsigned long)bpage); } EXPORT_SYMBOL_GPL(ring_buffer_free_read_page); /** * ring_buffer_read_page - extract a page from the ring buffer * @buffer: buffer to extract from * @data_page: the page to use allocated from ring_buffer_alloc_read_page * @len: amount to extract * @cpu: the cpu of the buffer to extract * @full: should the extraction only happen when the page is full. * * This function will pull out a page from the ring buffer and consume it. * @data_page must be the address of the variable that was returned * from ring_buffer_alloc_read_page. This is because the page might be used * to swap with a page in the ring buffer. * * for example: * rpage = ring_buffer_alloc_read_page(buffer, cpu); * if (IS_ERR(rpage)) * return PTR_ERR(rpage); * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0); * if (ret >= 0) * process_page(rpage, ret); * * When @full is set, the function will not return true unless * the writer is off the reader page. * * Note: it is up to the calling functions to handle sleeps and wakeups. * The ring buffer can be used anywhere in the kernel and can not * blindly call wake_up. The layer that uses the ring buffer must be * responsible for that. * * Returns: * >=0 if data has been transferred, returns the offset of consumed data. * <0 if no data has been transferred. */ int ring_buffer_read_page(struct ring_buffer *buffer, void **data_page, size_t len, int cpu, int full) { struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu]; struct ring_buffer_event *event; struct buffer_data_page *bpage; struct buffer_page *reader; unsigned long missed_events; unsigned long flags; unsigned int commit; unsigned int read; u64 save_timestamp; int ret = -1; if (!cpumask_test_cpu(cpu, buffer->cpumask)) goto out; /* * If len is not big enough to hold the page header, then * we can not copy anything. */ if (len <= BUF_PAGE_HDR_SIZE) goto out; len -= BUF_PAGE_HDR_SIZE; if (!data_page) goto out; bpage = *data_page; if (!bpage) goto out; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); reader = rb_get_reader_page(cpu_buffer); if (!reader) goto out_unlock; event = rb_reader_event(cpu_buffer); read = reader->read; commit = rb_page_commit(reader); /* Check if any events were dropped */ missed_events = cpu_buffer->lost_events; /* * If this page has been partially read or * if len is not big enough to read the rest of the page or * a writer is still on the page, then * we must copy the data from the page to the buffer. * Otherwise, we can simply swap the page with the one passed in. */ if (read || (len < (commit - read)) || cpu_buffer->reader_page == cpu_buffer->commit_page) { struct buffer_data_page *rpage = cpu_buffer->reader_page->page; unsigned int rpos = read; unsigned int pos = 0; unsigned int size; if (full) goto out_unlock; if (len > (commit - read)) len = (commit - read); /* Always keep the time extend and data together */ size = rb_event_ts_length(event); if (len < size) goto out_unlock; /* save the current timestamp, since the user will need it */ save_timestamp = cpu_buffer->read_stamp; /* Need to copy one event at a time */ do { /* We need the size of one event, because * rb_advance_reader only advances by one event, * whereas rb_event_ts_length may include the size of * one or two events. * We have already ensured there's enough space if this * is a time extend. */ size = rb_event_length(event); memcpy(bpage->data + pos, rpage->data + rpos, size); len -= size; rb_advance_reader(cpu_buffer); rpos = reader->read; pos += size; if (rpos >= commit) break; event = rb_reader_event(cpu_buffer); /* Always keep the time extend and data together */ size = rb_event_ts_length(event); } while (len >= size); /* update bpage */ local_set(&bpage->commit, pos); bpage->time_stamp = save_timestamp; /* we copied everything to the beginning */ read = 0; } else { /* update the entry counter */ cpu_buffer->read += rb_page_entries(reader); cpu_buffer->read_bytes += BUF_PAGE_SIZE; /* swap the pages */ rb_init_page(bpage); bpage = reader->page; reader->page = *data_page; local_set(&reader->write, 0); local_set(&reader->entries, 0); reader->read = 0; *data_page = bpage; /* * Use the real_end for the data size, * This gives us a chance to store the lost events * on the page. */ if (reader->real_end) local_set(&bpage->commit, reader->real_end); } ret = read; cpu_buffer->lost_events = 0; commit = local_read(&bpage->commit); /* * Set a flag in the commit field if we lost events */ if (missed_events) { /* If there is room at the end of the page to save the * missed events, then record it there. */ if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) { memcpy(&bpage->data[commit], &missed_events, sizeof(missed_events)); local_add(RB_MISSED_STORED, &bpage->commit); commit += sizeof(missed_events); } local_add(RB_MISSED_EVENTS, &bpage->commit); } /* * This page may be off to user land. Zero it out here. */ if (commit < BUF_PAGE_SIZE) memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit); out_unlock: raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); out: return ret; } EXPORT_SYMBOL_GPL(ring_buffer_read_page); /* * We only allocate new buffers, never free them if the CPU goes down. * If we were to free the buffer, then the user would lose any trace that was in * the buffer. */ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node) { struct ring_buffer *buffer; long nr_pages_same; int cpu_i; unsigned long nr_pages; buffer = container_of(node, struct ring_buffer, node); if (cpumask_test_cpu(cpu, buffer->cpumask)) return 0; nr_pages = 0; nr_pages_same = 1; /* check if all cpu sizes are same */ for_each_buffer_cpu(buffer, cpu_i) { /* fill in the size from first enabled cpu */ if (nr_pages == 0) nr_pages = buffer->buffers[cpu_i]->nr_pages; if (nr_pages != buffer->buffers[cpu_i]->nr_pages) { nr_pages_same = 0; break; } } /* allocate minimum pages, user can later expand it */ if (!nr_pages_same) nr_pages = 2; buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) { WARN(1, "failed to allocate ring buffer on CPU %u\n", cpu); return -ENOMEM; } smp_wmb(); cpumask_set_cpu(cpu, buffer->cpumask); return 0; } #ifdef CONFIG_RING_BUFFER_STARTUP_TEST /* * This is a basic integrity check of the ring buffer. * Late in the boot cycle this test will run when configured in. * It will kick off a thread per CPU that will go into a loop * writing to the per cpu ring buffer various sizes of data. * Some of the data will be large items, some small. * * Another thread is created that goes into a spin, sending out * IPIs to the other CPUs to also write into the ring buffer. * this is to test the nesting ability of the buffer. * * Basic stats are recorded and reported. If something in the * ring buffer should happen that's not expected, a big warning * is displayed and all ring buffers are disabled. */ static struct task_struct *rb_threads[NR_CPUS] __initdata; struct rb_test_data { struct ring_buffer *buffer; unsigned long events; unsigned long bytes_written; unsigned long bytes_alloc; unsigned long bytes_dropped; unsigned long events_nested; unsigned long bytes_written_nested; unsigned long bytes_alloc_nested; unsigned long bytes_dropped_nested; int min_size_nested; int max_size_nested; int max_size; int min_size; int cpu; int cnt; }; static struct rb_test_data rb_data[NR_CPUS] __initdata; /* 1 meg per cpu */ #define RB_TEST_BUFFER_SIZE 1048576 static char rb_string[] __initdata = "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\" "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890" "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv"; static bool rb_test_started __initdata; struct rb_item { int size; char str[]; }; static __init int rb_write_something(struct rb_test_data *data, bool nested) { struct ring_buffer_event *event; struct rb_item *item; bool started; int event_len; int size; int len; int cnt; /* Have nested writes different that what is written */ cnt = data->cnt + (nested ? 27 : 0); /* Multiply cnt by ~e, to make some unique increment */ size = (data->cnt * 68 / 25) % (sizeof(rb_string) - 1); len = size + sizeof(struct rb_item); started = rb_test_started; /* read rb_test_started before checking buffer enabled */ smp_rmb(); event = ring_buffer_lock_reserve(data->buffer, len); if (!event) { /* Ignore dropped events before test starts. */ if (started) { if (nested) data->bytes_dropped += len; else data->bytes_dropped_nested += len; } return len; } event_len = ring_buffer_event_length(event); if (RB_WARN_ON(data->buffer, event_len < len)) goto out; item = ring_buffer_event_data(event); item->size = size; memcpy(item->str, rb_string, size); if (nested) { data->bytes_alloc_nested += event_len; data->bytes_written_nested += len; data->events_nested++; if (!data->min_size_nested || len < data->min_size_nested) data->min_size_nested = len; if (len > data->max_size_nested) data->max_size_nested = len; } else { data->bytes_alloc += event_len; data->bytes_written += len; data->events++; if (!data->min_size || len < data->min_size) data->max_size = len; if (len > data->max_size) data->max_size = len; } out: ring_buffer_unlock_commit(data->buffer, event); return 0; } static __init int rb_test(void *arg) { struct rb_test_data *data = arg; while (!kthread_should_stop()) { rb_write_something(data, false); data->cnt++; set_current_state(TASK_INTERRUPTIBLE); /* Now sleep between a min of 100-300us and a max of 1ms */ usleep_range(((data->cnt % 3) + 1) * 100, 1000); } return 0; } static __init void rb_ipi(void *ignore) { struct rb_test_data *data; int cpu = smp_processor_id(); data = &rb_data[cpu]; rb_write_something(data, true); } static __init int rb_hammer_test(void *arg) { while (!kthread_should_stop()) { /* Send an IPI to all cpus to write data! */ smp_call_function(rb_ipi, NULL, 1); /* No sleep, but for non preempt, let others run */ schedule(); } return 0; } static __init int test_ringbuffer(void) { struct task_struct *rb_hammer; struct ring_buffer *buffer; int cpu; int ret = 0; pr_info("Running ring buffer tests...\n"); buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE); if (WARN_ON(!buffer)) return 0; /* Disable buffer so that threads can't write to it yet */ ring_buffer_record_off(buffer); for_each_online_cpu(cpu) { rb_data[cpu].buffer = buffer; rb_data[cpu].cpu = cpu; rb_data[cpu].cnt = cpu; rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu], "rbtester/%d", cpu); if (WARN_ON(IS_ERR(rb_threads[cpu]))) { pr_cont("FAILED\n"); ret = PTR_ERR(rb_threads[cpu]); goto out_free; } kthread_bind(rb_threads[cpu], cpu); wake_up_process(rb_threads[cpu]); } /* Now create the rb hammer! */ rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer"); if (WARN_ON(IS_ERR(rb_hammer))) { pr_cont("FAILED\n"); ret = PTR_ERR(rb_hammer); goto out_free; } ring_buffer_record_on(buffer); /* * Show buffer is enabled before setting rb_test_started. * Yes there's a small race window where events could be * dropped and the thread wont catch it. But when a ring * buffer gets enabled, there will always be some kind of * delay before other CPUs see it. Thus, we don't care about * those dropped events. We care about events dropped after * the threads see that the buffer is active. */ smp_wmb(); rb_test_started = true; set_current_state(TASK_INTERRUPTIBLE); /* Just run for 10 seconds */; schedule_timeout(10 * HZ); kthread_stop(rb_hammer); out_free: for_each_online_cpu(cpu) { if (!rb_threads[cpu]) break; kthread_stop(rb_threads[cpu]); } if (ret) { ring_buffer_free(buffer); return ret; } /* Report! */ pr_info("finished\n"); for_each_online_cpu(cpu) { struct ring_buffer_event *event; struct rb_test_data *data = &rb_data[cpu]; struct rb_item *item; unsigned long total_events; unsigned long total_dropped; unsigned long total_written; unsigned long total_alloc; unsigned long total_read = 0; unsigned long total_size = 0; unsigned long total_len = 0; unsigned long total_lost = 0; unsigned long lost; int big_event_size; int small_event_size; ret = -1; total_events = data->events + data->events_nested; total_written = data->bytes_written + data->bytes_written_nested; total_alloc = data->bytes_alloc + data->bytes_alloc_nested; total_dropped = data->bytes_dropped + data->bytes_dropped_nested; big_event_size = data->max_size + data->max_size_nested; small_event_size = data->min_size + data->min_size_nested; pr_info("CPU %d:\n", cpu); pr_info(" events: %ld\n", total_events); pr_info(" dropped bytes: %ld\n", total_dropped); pr_info(" alloced bytes: %ld\n", total_alloc); pr_info(" written bytes: %ld\n", total_written); pr_info(" biggest event: %d\n", big_event_size); pr_info(" smallest event: %d\n", small_event_size); if (RB_WARN_ON(buffer, total_dropped)) break; ret = 0; while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) { total_lost += lost; item = ring_buffer_event_data(event); total_len += ring_buffer_event_length(event); total_size += item->size + sizeof(struct rb_item); if (memcmp(&item->str[0], rb_string, item->size) != 0) { pr_info("FAILED!\n"); pr_info("buffer had: %.*s\n", item->size, item->str); pr_info("expected: %.*s\n", item->size, rb_string); RB_WARN_ON(buffer, 1); ret = -1; break; } total_read++; } if (ret) break; ret = -1; pr_info(" read events: %ld\n", total_read); pr_info(" lost events: %ld\n", total_lost); pr_info(" total events: %ld\n", total_lost + total_read); pr_info(" recorded len bytes: %ld\n", total_len); pr_info(" recorded size bytes: %ld\n", total_size); if (total_lost) pr_info(" With dropped events, record len and size may not match\n" " alloced and written from above\n"); if (!total_lost) { if (RB_WARN_ON(buffer, total_len != total_alloc || total_size != total_written)) break; } if (RB_WARN_ON(buffer, total_lost + total_read != total_events)) break; ret = 0; } if (!ret) pr_info("Ring buffer PASSED!\n"); ring_buffer_free(buffer); return 0; } late_initcall(test_ringbuffer); #endif /* CONFIG_RING_BUFFER_STARTUP_TEST */
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