From e65ac2bdda549dd3411731ad37c17460e4ee1bae Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Google)" Date: Thu, 20 Oct 2022 23:14:27 -0400 Subject: [PATCH] tracing/ring-buffer: Have polling block on watermark commit 42fb0a1e84ff525ebe560e2baf9451ab69127e2b upstream. Currently the way polling works on the ring buffer is broken. It will return immediately if there's any data in the ring buffer whereas a read will block until the watermark (defined by the tracefs buffer_percent file) is hit. That is, a select() or poll() will return as if there's data available, but then the following read will block. This is broken for the way select()s and poll()s are supposed to work. Have the polling on the ring buffer also block the same way reads and splice does on the ring buffer. Link: https://lkml.kernel.org/r/20221020231427.41be3f26@gandalf.local.home Cc: Linux Trace Kernel Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Primiano Tucci Cc: stable@vger.kernel.org Fixes: 1e0d6714aceb7 ("ring-buffer: Do not wake up a splice waiter when page is not full") Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- include/linux/ring_buffer.h | 2 +- kernel/trace/ring_buffer.c | 54 ++++++++++++++++++++++++------------- kernel/trace/trace.c | 2 +- 3 files changed, 37 insertions(+), 21 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 1a40277b512c..b73950772299 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -99,7 +99,7 @@ __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *k int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full); __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu, - struct file *filp, poll_table *poll_table); + struct file *filp, poll_table *poll_table, int full); #define RING_BUFFER_ALL_CPUS -1 diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index c4234430afea..176d858903bd 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -566,6 +566,21 @@ size_t ring_buffer_nr_dirty_pages(struct ring_buffer *buffer, int cpu) return cnt - read; } +static __always_inline bool full_hit(struct ring_buffer *buffer, int cpu, int full) +{ + struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu]; + size_t nr_pages; + size_t dirty; + + nr_pages = cpu_buffer->nr_pages; + if (!nr_pages || !full) + return true; + + dirty = ring_buffer_nr_dirty_pages(buffer, cpu); + + return (dirty * 100) > (full * nr_pages); +} + /* * rb_wake_up_waiters - wake up tasks waiting for ring buffer input * @@ -661,22 +676,20 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full) !ring_buffer_empty_cpu(buffer, cpu)) { unsigned long flags; bool pagebusy; - size_t nr_pages; - size_t dirty; + bool done; if (!full) break; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page; - nr_pages = cpu_buffer->nr_pages; - dirty = ring_buffer_nr_dirty_pages(buffer, cpu); + done = !pagebusy && full_hit(buffer, cpu, full); + if (!cpu_buffer->shortest_full || cpu_buffer->shortest_full > full) cpu_buffer->shortest_full = full; raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); - if (!pagebusy && - (!nr_pages || (dirty * 100) > full * nr_pages)) + if (done) break; } @@ -697,6 +710,7 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full) * @cpu: the cpu buffer to wait on * @filp: the file descriptor * @poll_table: The poll descriptor + * @full: wait until the percentage of pages are 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 @@ -706,14 +720,14 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full) * zero otherwise. */ __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu, - struct file *filp, poll_table *poll_table) + struct file *filp, poll_table *poll_table, int full) { struct ring_buffer_per_cpu *cpu_buffer; struct rb_irq_work *work; - if (cpu == RING_BUFFER_ALL_CPUS) + if (cpu == RING_BUFFER_ALL_CPUS) { work = &buffer->irq_work; - else { + } else { if (!cpumask_test_cpu(cpu, buffer->cpumask)) return -EINVAL; @@ -721,8 +735,14 @@ __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu, work = &cpu_buffer->irq_work; } - poll_wait(filp, &work->waiters, poll_table); - work->waiters_pending = true; + if (full) { + poll_wait(filp, &work->full_waiters, poll_table); + work->full_waiters_pending = true; + } else { + 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 @@ -738,6 +758,9 @@ __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu, */ smp_mb(); + if (full) + return full_hit(buffer, cpu, full) ? EPOLLIN | EPOLLRDNORM : 0; + if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) || (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu))) return EPOLLIN | EPOLLRDNORM; @@ -2640,10 +2663,6 @@ static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer, static __always_inline void rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) { - size_t nr_pages; - size_t dirty; - size_t full; - if (buffer->irq_work.waiters_pending) { buffer->irq_work.waiters_pending = false; /* irq_work_queue() supplies it's own memory barriers */ @@ -2667,10 +2686,7 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched); - full = cpu_buffer->shortest_full; - nr_pages = cpu_buffer->nr_pages; - dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu); - if (full && nr_pages && (dirty * 100) <= full * nr_pages) + if (!full_hit(buffer, cpu_buffer->cpu, cpu_buffer->shortest_full)) return; cpu_buffer->irq_work.wakeup_full = true; diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 62fd8798b0c4..42f45665e059 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5993,7 +5993,7 @@ trace_poll(struct trace_iterator *iter, struct file *filp, poll_table *poll_tabl return EPOLLIN | EPOLLRDNORM; else return ring_buffer_poll_wait(iter->trace_buffer->buffer, iter->cpu_file, - filp, poll_table); + filp, poll_table, iter->tr->buffer_percent); } static __poll_t