diff options
| author | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2020-03-17 22:32:28 +0100 |
|---|---|---|
| committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2020-03-20 00:11:19 +0100 |
| commit | ff84c50cfb4b8dc68c982fb6c05a524e1539ee2f (patch) | |
| tree | 63fff4f557b19618a9d4bcc8e224f111c2300226 /kernel | |
| parent | ring-buffer: Have rb_iter_head_event() handle concurrent writer (diff) | |
| download | linux-ff84c50cfb4b8dc68c982fb6c05a524e1539ee2f.tar.xz linux-ff84c50cfb4b8dc68c982fb6c05a524e1539ee2f.zip | |
ring-buffer: Do not die if rb_iter_peek() fails more than thrice
As the iterator will be reading a live buffer, and if the event being read
is on a page that a writer crosses, it will fail and try again, the
condition in rb_iter_peek() that only allows a retry to happen three times
is no longer valid. Allow rb_iter_peek() to retry more than three times
without killing the ring buffer, but only if rb_iter_head_event() had failed
at least once.
Link: http://lkml.kernel.org/r/20200317213416.452888193@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/ring_buffer.c | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3d718add73c1..475338fda969 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4012,6 +4012,7 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts) struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_event *event; int nr_loops = 0; + bool failed = false; if (ts) *ts = 0; @@ -4038,10 +4039,14 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts) * 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). + * We should never hit the following condition more than thrice, + * unless the buffer is very small, and there's a writer + * that is causing the reader to fail getting an event. */ - if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) + if (++nr_loops > 3) { + RB_WARN_ON(cpu_buffer, !failed); return NULL; + } if (rb_per_cpu_empty(cpu_buffer)) return NULL; @@ -4052,8 +4057,10 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts) } event = rb_iter_head_event(iter); - if (!event) + if (!event) { + failed = true; goto again; + } switch (event->type_len) { case RINGBUF_TYPE_PADDING: |