diff options
Diffstat (limited to 'kernel/trace/ring_buffer.c')
| -rw-r--r-- | kernel/trace/ring_buffer.c | 67 |
1 files changed, 38 insertions, 29 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index fc4da2d97f9b..da41de9dc319 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -543,7 +543,7 @@ static void rb_wake_up_waiters(struct irq_work *work) * 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. */ -void ring_buffer_wait(struct ring_buffer *buffer, int cpu) +int ring_buffer_wait(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; DEFINE_WAIT(wait); @@ -557,6 +557,8 @@ void ring_buffer_wait(struct ring_buffer *buffer, int cpu) if (cpu == RING_BUFFER_ALL_CPUS) work = &buffer->irq_work; else { + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -ENODEV; cpu_buffer = buffer->buffers[cpu]; work = &cpu_buffer->irq_work; } @@ -591,6 +593,7 @@ void ring_buffer_wait(struct ring_buffer *buffer, int cpu) schedule(); finish_wait(&work->waiters, &wait); + return 0; } /** @@ -613,10 +616,6 @@ int ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu, struct ring_buffer_per_cpu *cpu_buffer; struct rb_irq_work *work; - if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) || - (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu))) - return POLLIN | POLLRDNORM; - if (cpu == RING_BUFFER_ALL_CPUS) work = &buffer->irq_work; else { @@ -627,8 +626,22 @@ int ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu, work = &cpu_buffer->irq_work; } - work->waiters_pending = true; 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))) @@ -1982,7 +1995,7 @@ rb_add_time_stamp(struct ring_buffer_event *event, u64 delta) /** * rb_update_event - update event type and data - * @event: the even to update + * @event: the event to update * @type: the type of event * @length: the size of the event field in the ring buffer * @@ -2638,7 +2651,7 @@ static DEFINE_PER_CPU(unsigned int, current_context); static __always_inline int trace_recursive_lock(void) { - unsigned int val = this_cpu_read(current_context); + unsigned int val = __this_cpu_read(current_context); int bit; if (in_interrupt()) { @@ -2655,18 +2668,17 @@ static __always_inline int trace_recursive_lock(void) return 1; val |= (1 << bit); - this_cpu_write(current_context, val); + __this_cpu_write(current_context, val); return 0; } static __always_inline void trace_recursive_unlock(void) { - unsigned int val = this_cpu_read(current_context); + unsigned int val = __this_cpu_read(current_context); - val--; - val &= this_cpu_read(current_context); - this_cpu_write(current_context, val); + val &= val & (val - 1); + __this_cpu_write(current_context, val); } #else @@ -3355,21 +3367,16 @@ 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 */ - if (list_empty(&cpu_buffer->reader_page->list)) { - iter->head_page = rb_set_head_page(cpu_buffer); - if (unlikely(!iter->head_page)) - return; - iter->head = iter->head_page->read; - } else { - iter->head_page = cpu_buffer->reader_page; - iter->head = cpu_buffer->reader_page->read; - } + 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; - iter->cache_reader_page = cpu_buffer->reader_page; - iter->cache_read = cpu_buffer->read; } /** @@ -3762,12 +3769,14 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts) return NULL; /* - * 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). + * 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 > 2)) + if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) return NULL; if (rb_per_cpu_empty(cpu_buffer)) |