diff options
Diffstat (limited to 'kernel/trace/ring_buffer.c')
| -rw-r--r-- | kernel/trace/ring_buffer.c | 5014 |
1 files changed, 5014 insertions, 0 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c new file mode 100644 index 000000000..0315d4317 --- /dev/null +++ b/kernel/trace/ring_buffer.c @@ -0,0 +1,5014 @@ +/* + * Generic ring buffer + * + * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com> + */ +#include <linux/ftrace_event.h> +#include <linux/ring_buffer.h> +#include <linux/trace_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/kmemcheck.h> +#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 <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, "\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. + * + */ + +/* + * A fast way to enable or disable all ring buffers is to + * call tracing_on or tracing_off. Turning off the ring buffers + * prevents all ring buffers from being recorded to. + * Turning this switch on, makes it OK to write to the + * ring buffer, if the ring buffer is enabled itself. + * + * There's three layers that must be on in order to write + * to the ring buffer. + * + * 1) This global flag must be set. + * 2) The ring buffer must be enabled for recording. + * 3) The per cpu buffer must be enabled for recording. + * + * In case of an anomaly, this global flag has a bit set that + * will permantly disable all ring buffers. + */ + +/* + * Global flag to disable all recording to ring buffers + * This has two bits: ON, DISABLED + * + * ON DISABLED + * ---- ---------- + * 0 0 : ring buffers are off + * 1 0 : ring buffers are on + * X 1 : ring buffers are permanently disabled + */ + +enum { + RB_BUFFERS_ON_BIT = 0, + RB_BUFFERS_DISABLED_BIT = 1, +}; + +enum { + RB_BUFFERS_ON = 1 << RB_BUFFERS_ON_BIT, + RB_BUFFERS_DISABLED = 1 << RB_BUFFERS_DISABLED_BIT, +}; + +static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON; + +/* Used for individual buffers (after the counter) */ +#define RB_BUFFER_OFF (1 << 20) + +#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data) + +/** + * tracing_off_permanent - permanently disable ring buffers + * + * This function, once called, will disable all ring buffers + * permanently. + */ +void tracing_off_permanent(void) +{ + set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags); +} + +#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 = 16, +}; + +#define skip_time_extend(event) \ + ((struct ring_buffer_event *)((char *)event + RB_LEN_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 (event->type_len == RINGBUF_TYPE_TIME_EXTEND) { + /* 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 (event->type_len == RINGBUF_TYPE_TIME_EXTEND) + 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 void * +rb_event_data(struct ring_buffer_event *event) +{ + if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) + 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) + +/* Flag when events were overwritten */ +#define RB_MISSED_EVENTS (1 << 31) +/* Missed count stored at end */ +#define RB_MISSED_STORED (1 << 30) + +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) +{ + return local_read(&((struct buffer_data_page *)page)->commit) + + 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; +}; + +/* + * 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; + unsigned int nr_pages; + 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; + 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 */ + int 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; + +#ifdef CONFIG_HOTPLUG_CPU + struct notifier_block cpu_notify; +#endif + u64 (*clock)(void); + + struct rb_irq_work irq_work; +}; + +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 POLLIN | POLLRDNORM if data exists in the buffers, + * zero otherwise. + */ +int 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 POLLIN | POLLRDNORM; + 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 + * temporarially. + */ + +#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 int 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_dactivate - 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 + * + * Returns 1 if moved tail page, 0 if someone else did. + */ +static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer, + struct buffer_page *tail_page, + struct buffer_page *next_page) +{ + struct buffer_page *old_tail; + unsigned long old_entries; + unsigned long old_write; + int ret = 0; + + /* + * 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 == 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); + + old_tail = cmpxchg(&cpu_buffer->tail_page, + tail_page, next_page); + + if (old_tail == tail_page) + ret = 1; + } + + return ret; +} + +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(int nr_pages, struct list_head *pages, int cpu) +{ + int i; + struct buffer_page *bpage, *tmp; + + for (i = 0; i < nr_pages; i++) { + struct page *page; + /* + * __GFP_NORETRY flag makes sure that the allocation fails + * gracefully without invoking oom-killer and the system is + * not destabilized. + */ + bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), + GFP_KERNEL | __GFP_NORETRY, + cpu_to_node(cpu)); + if (!bpage) + goto free_pages; + + list_add(&bpage->list, pages); + + page = alloc_pages_node(cpu_to_node(cpu), + GFP_KERNEL | __GFP_NORETRY, 0); + if (!page) + goto free_pages; + bpage->page = page_address(page); + rb_init_page(bpage->page); + } + + return 0; + +free_pages: + list_for_each_entry_safe(bpage, tmp, pages, list) { + list_del_init(&bpage->list); + free_buffer_page(bpage); + } + + return -ENOMEM; +} + +static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer, + unsigned 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, int 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); +} + +#ifdef CONFIG_HOTPLUG_CPU +static int rb_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu); +#endif + +/** + * __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; + int bsize; + int cpu, nr_pages; + + /* keep it in its own cache line */ + buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()), + GFP_KERNEL); + if (!buffer) + return NULL; + + if (!alloc_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; + + /* + * In case of non-hotplug cpu, if the ring-buffer is allocated + * in early initcall, it will not be notified of secondary cpus. + * In that off case, we need to allocate for all possible cpus. + */ +#ifdef CONFIG_HOTPLUG_CPU + cpu_notifier_register_begin(); + cpumask_copy(buffer->cpumask, cpu_online_mask); +#else + cpumask_copy(buffer->cpumask, cpu_possible_mask); +#endif + 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; + + for_each_buffer_cpu(buffer, cpu) { + buffer->buffers[cpu] = + rb_allocate_cpu_buffer(buffer, nr_pages, cpu); + if (!buffer->buffers[cpu]) + goto fail_free_buffers; + } + +#ifdef CONFIG_HOTPLUG_CPU + buffer->cpu_notify.notifier_call = rb_cpu_notify; + buffer->cpu_notify.priority = 0; + __register_cpu_notifier(&buffer->cpu_notify); + cpu_notifier_register_done(); +#endif + + 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); +#ifdef CONFIG_HOTPLUG_CPU + cpu_notifier_register_done(); +#endif + + 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; + +#ifdef CONFIG_HOTPLUG_CPU + cpu_notifier_register_begin(); + __unregister_cpu_notifier(&buffer->cpu_notify); +#endif + + for_each_buffer_cpu(buffer, cpu) + rb_free_cpu_buffer(buffer->buffers[cpu]); + +#ifdef CONFIG_HOTPLUG_CPU + cpu_notifier_register_done(); +#endif + + 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; +} + +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 int 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 int 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 { + 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 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; + + size = DIV_ROUND_UP(size, BUF_PAGE_SIZE); + size *= BUF_PAGE_SIZE; + + /* we need a minimum of two pages */ + if (size < BUF_PAGE_SIZE * 2) + size = BUF_PAGE_SIZE * 2; + + nr_pages = DIV_ROUND_UP(size, 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 intitialized */ + 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 inline void * +__rb_data_page_index(struct buffer_data_page *bpage, unsigned index) +{ + return bpage->data + index; +} + +static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index) +{ + return bpage->page->data + index; +} + +static 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 inline struct ring_buffer_event * +rb_iter_head_event(struct ring_buffer_iter *iter) +{ + return __rb_page_index(iter->head_page, iter->head); +} + +static inline unsigned rb_page_commit(struct buffer_page *bpage) +{ + return local_read(&bpage->page->commit); +} + +/* Size is determined by what has been committed */ +static inline unsigned rb_page_size(struct buffer_page *bpage) +{ + return rb_page_commit(bpage); +} + +static inline unsigned +rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer) +{ + return rb_page_commit(cpu_buffer->commit_page); +} + +static 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 inline int +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 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 != 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); + 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 != cpu_buffer->tail_page)) + goto again; +} + +static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp; + cpu_buffer->reader_page->read = 0; +} + +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; +} + +/* Slow path, do not inline */ +static noinline struct ring_buffer_event * +rb_add_time_stamp(struct ring_buffer_event *event, u64 delta) +{ + event->type_len = RINGBUF_TYPE_TIME_EXTEND; + + /* Not the first event on the page? */ + if (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); +} + +/** + * 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, unsigned length, + int add_timestamp, u64 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 resevered space. + */ + if (unlikely(add_timestamp)) { + event = rb_add_time_stamp(event, delta); + 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); +} + +/* + * 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) { + /* + * If the tail had moved passed next, then we need + * to reset the pointer. + */ + if (cpu_buffer->tail_page != tail_page && + cpu_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 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 = 1; + + 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); + + return length; +} + +static inline void +rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer, + struct buffer_page *tail_page, + unsigned long tail, unsigned long length) +{ + struct ring_buffer_event *event; + + /* + * 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); + kmemcheck_annotate_bitfield(event, bitfield); + + /* 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); +} + +/* + * 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 length, unsigned long tail, + struct buffer_page *tail_page, u64 ts) +{ + 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; + } + } + } + + ret = rb_tail_page_update(cpu_buffer, tail_page, next_page); + if (ret) { + /* + * Nested commits always have zero deltas, so + * just reread the time stamp + */ + ts = rb_time_stamp(buffer); + next_page->page->time_stamp = ts; + } + + out_again: + + rb_reset_tail(cpu_buffer, tail_page, tail, length); + + /* fail and let the caller try again */ + return ERR_PTR(-EAGAIN); + + out_reset: + /* reset write */ + rb_reset_tail(cpu_buffer, tail_page, tail, length); + + return NULL; +} + +static struct ring_buffer_event * +__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long length, u64 ts, + u64 delta, int add_timestamp) +{ + struct buffer_page *tail_page; + struct ring_buffer_event *event; + 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(add_timestamp)) + length += RB_LEN_TIME_EXTEND; + + tail_page = cpu_buffer->tail_page; + write = local_add_return(length, &tail_page->write); + + /* set write to only the index of the write */ + write &= RB_WRITE_MASK; + tail = write - length; + + /* + * If this is the first commit on the page, then it has the same + * timestamp as the page itself. + */ + if (!tail) + 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, length, tail, + tail_page, ts); + + /* We reserved something on the buffer */ + + event = __rb_page_index(tail_page, tail); + kmemcheck_annotate_bitfield(event, bitfield); + rb_update_event(cpu_buffer, event, length, add_timestamp, delta); + + 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 = ts; + + /* account for these added bytes */ + local_add(length, &cpu_buffer->entries_bytes); + + return event; +} + +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 = 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 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 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; + u64 ts, delta; + int nr_loops = 0; + int add_timestamp; + 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(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) { + local_dec(&cpu_buffer->committing); + local_dec(&cpu_buffer->commits); + return NULL; + } +#endif + + length = rb_calculate_event_length(length); + again: + add_timestamp = 0; + 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; + + ts = rb_time_stamp(cpu_buffer->buffer); + diff = ts - cpu_buffer->write_stamp; + + /* make sure this diff is calculated here */ + barrier(); + + /* Did the write stamp get updated already? */ + if (likely(ts >= cpu_buffer->write_stamp)) { + delta = diff; + if (unlikely(test_time_stamp(delta))) { + int local_clock_stable = 1; +#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK + local_clock_stable = sched_clock_stable(); +#endif + WARN_ONCE(delta > (1ULL << 59), + KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s", + (unsigned long long)delta, + (unsigned long long)ts, + (unsigned long long)cpu_buffer->write_stamp, + local_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"); + add_timestamp = 1; + } + } + + event = __rb_reserve_next(cpu_buffer, length, ts, + delta, add_timestamp); + if (unlikely(PTR_ERR(event) == -EAGAIN)) + goto again; + + if (!event) + goto out_fail; + + return event; + + out_fail: + rb_end_commit(cpu_buffer); + return NULL; +} + +#ifdef CONFIG_TRACING + +/* + * 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 DEFINE_PER_CPU(unsigned int, current_context); + +static __always_inline int trace_recursive_lock(void) +{ + unsigned int val = __this_cpu_read(current_context); + int bit; + + if (in_interrupt()) { + if (in_nmi()) + bit = 0; + else if (in_irq()) + bit = 1; + else + bit = 2; + } else + bit = 3; + + if (unlikely(val & (1 << bit))) + return 1; + + val |= (1 << bit); + __this_cpu_write(current_context, val); + + return 0; +} + +static __always_inline void trace_recursive_unlock(void) +{ + __this_cpu_and(current_context, __this_cpu_read(current_context) - 1); +} + +#else + +#define trace_recursive_lock() (0) +#define trace_recursive_unlock() do { } while (0) + +#endif + +/** + * 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 reseverd 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 (ring_buffer_flags != RB_BUFFERS_ON) + return NULL; + + /* If we are tracing schedule, we don't want to recurse */ + preempt_disable_notrace(); + + if (atomic_read(&buffer->record_disabled)) + goto out_nocheck; + + if (trace_recursive_lock()) + goto out_nocheck; + + 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; + + event = rb_reserve_next_event(buffer, cpu_buffer, length); + if (!event) + goto out; + + return event; + + out: + trace_recursive_unlock(); + + out_nocheck: + preempt_enable_notrace(); + return NULL; +} +EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve); + +static 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 = event->array[0]; + delta <<= TS_SHIFT; + delta += event->time_delta; + 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); + } +} + +/** + * 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(); + + preempt_enable_notrace(); + + return 0; +} +EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit); + +static inline void rb_event_discard(struct ring_buffer_event *event) +{ + if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) + 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; +} + +/* + * 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 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(); + + 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; + + if (ring_buffer_flags != RB_BUFFERS_ON) + return -EBUSY; + + 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; + + event = rb_reserve_next_event(buffer, cpu_buffer, length); + if (!event) + goto out; + + body = rb_event_data(event); + + memcpy(body, data, length); + + rb_commit(cpu_buffer, event); + + rb_wakeups(buffer, cpu_buffer); + + ret = 0; + out: + preempt_enable_notrace(); + + return ret; +} +EXPORT_SYMBOL_GPL(ring_buffer_write); + +static int 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 1; + + 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. + */ +int ring_buffer_record_is_on(struct ring_buffer *buffer) +{ + return !atomic_read(&buffer->record_disabled); +} + +/** + * 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; + + cpu_buffer = iter->cpu_buffer; + + return iter->head_page == cpu_buffer->commit_page && + iter->head == rb_commit_index(cpu_buffer); +} +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 = event->array[0]; + delta <<= TS_SHIFT; + delta += event->time_delta; + cpu_buffer->read_stamp += delta; + return; + + case RINGBUF_TYPE_TIME_STAMP: + /* FIXME: not implemented */ + 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 = event->array[0]; + delta <<= TS_SHIFT; + delta += event->time_delta; + iter->read_stamp += delta; + return; + + case RINGBUF_TYPE_TIME_STAMP: + /* FIXME: not implemented */ + 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; + rb_reset_reader_page(cpu_buffer); + + if (overwrite != cpu_buffer->last_overrun) { + cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun; + cpu_buffer->last_overrun = overwrite; + } + + goto again; + + out: + 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; + + 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: + /* FIXME: not implemented */ + rb_advance_reader(cpu_buffer); + goto again; + + case RINGBUF_TYPE_DATA: + if (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; + + 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: + /* FIXME: not implemented */ + rb_advance_iter(iter); + goto again; + + case RINGBUF_TYPE_DATA: + if (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 int rb_ok_to_lock(void) +{ + /* + * If an NMI die dumps out the content of the ring buffer + * do not grab locks. We also permanently disable the ring + * buffer too. A one time deal is all you get from reading + * the ring buffer from an NMI. + */ + if (likely(!in_nmi())) + return 1; + + tracing_off_permanent(); + return 0; +} + +/** + * 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; + int dolock; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return NULL; + + dolock = rb_ok_to_lock(); + again: + local_irq_save(flags); + if (dolock) + raw_spin_lock(&cpu_buffer->reader_lock); + event = rb_buffer_peek(cpu_buffer, ts, lost_events); + if (event && event->type_len == RINGBUF_TYPE_PADDING) + rb_advance_reader(cpu_buffer); + if (dolock) + raw_spin_unlock(&cpu_buffer->reader_lock); + 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; + int dolock; + + dolock = rb_ok_to_lock(); + + 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); + if (dolock) + raw_spin_lock(&cpu_buffer->reader_lock); + + event = rb_buffer_peek(cpu_buffer, ts, lost_events); + if (event) { + cpu_buffer->lost_events = 0; + rb_advance_reader(cpu_buffer); + } + + if (dolock) + raw_spin_unlock(&cpu_buffer->reader_lock); + 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 recordng 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 + */ +int ring_buffer_empty(struct ring_buffer *buffer) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags; + int dolock; + int cpu; + int ret; + + dolock = rb_ok_to_lock(); + + /* 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); + if (dolock) + raw_spin_lock(&cpu_buffer->reader_lock); + ret = rb_per_cpu_empty(cpu_buffer); + if (dolock) + raw_spin_unlock(&cpu_buffer->reader_lock); + local_irq_restore(flags); + + if (!ret) + return 0; + } + + return 1; +} +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 + */ +int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags; + int dolock; + int ret; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return 1; + + dolock = rb_ok_to_lock(); + + cpu_buffer = buffer->buffers[cpu]; + local_irq_save(flags); + if (dolock) + raw_spin_lock(&cpu_buffer->reader_lock); + ret = rb_per_cpu_empty(cpu_buffer); + if (dolock) + raw_spin_unlock(&cpu_buffer->reader_lock); + 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 (ring_buffer_flags != RB_BUFFERS_ON) + goto out; + + 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 NULL on error. + */ +void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu) +{ + struct buffer_data_page *bpage; + struct page *page; + + page = alloc_pages_node(cpu_to_node(cpu), + GFP_KERNEL | __GFP_NORETRY, 0); + if (!page) + return NULL; + + bpage = page_address(page); + + 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 + * @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, void *data) +{ + free_page((unsigned long)data); +} +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 (!rpage) + * return error; + * 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); + +#ifdef CONFIG_HOTPLUG_CPU +static int rb_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + struct ring_buffer *buffer = + container_of(self, struct ring_buffer, cpu_notify); + long cpu = (long)hcpu; + int cpu_i, nr_pages_same; + unsigned int nr_pages; + + switch (action) { + case CPU_UP_PREPARE: + case CPU_UP_PREPARE_FROZEN: + if (cpumask_test_cpu(cpu, buffer->cpumask)) + return NOTIFY_OK; + + 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 %ld\n", + cpu); + return NOTIFY_OK; + } + smp_wmb(); + cpumask_set_cpu(cpu, buffer->cpumask); + break; + case CPU_DOWN_PREPARE: + case CPU_DOWN_PREPARE_FROZEN: + /* + * Do nothing. + * If we were to free the buffer, then the user would + * lose any trace that was in the buffer. + */ + break; + default: + break; + } + return NOTIFY_OK; +} +#endif + +#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(!rb_threads[cpu])) { + pr_cont("FAILED\n"); + ret = -1; + 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(!rb_hammer)) { + pr_cont("FAILED\n"); + ret = -1; + 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 */ |