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| author |   Peter Zijlstra <peterz@infradead.org> | 2019-05-17 13:52:32 +0200 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2019-05-24 09:00:10 +0200 |
| commit | 3f9fbe9bd86c534eba2faf5d840fd44c6049f50e (patch) | |
| tree | 5cc136bff2584bd31820c501b82c07dc72c37aa8 /kernel | |
| parent | perf/ring_buffer: Fix exposing a temporarily decreased data_head (diff) | |
| download | linux-dev-3f9fbe9bd86c534eba2faf5d840fd44c6049f50e.tar.xz linux-dev-3f9fbe9bd86c534eba2faf5d840fd44c6049f50e.zip | |
perf/ring_buffer: Add ordering to rb->nest increment
Similar to how decrementing rb->next too early can cause data_head to
(temporarily) be observed to go backward, so too can this happen when
we increment too late.
This barrier() ensures the rb->head load happens after the increment,
both the one in the 'goto again' path, as the one from
perf_output_get_handle() -- albeit very unlikely to matter for the
latter.
Suggested-by: Yabin Cui <yabinc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Cc: mark.rutland@arm.com
Cc: namhyung@kernel.org
Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing IRQ-disables")
Link: http://lkml.kernel.org/r/20190517115418.309516009@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/events/ring_buffer.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 009467a60578..4b5f8d932400 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -48,6 +48,15 @@ static void perf_output_put_handle(struct perf_output_handle *handle) unsigned long head; again: + /* + * In order to avoid publishing a head value that goes backwards, + * we must ensure the load of @rb->head happens after we've + * incremented @rb->nest. + * + * Otherwise we can observe a @rb->head value before one published + * by an IRQ/NMI happening between the load and the increment. + */ + barrier(); head = local_read(&rb->head); /* |