diff options
authorPeter Zijlstra <peterz@infradead.org>2019-05-17 13:52:32 +0200
committerPaul Gortmaker <paul.gortmaker@windriver.com>2019-09-16 12:21:35 -0400
commit286bf322a667753c01cf50340c17548985085c63 (patch)
parente1fdf22e0fffa8265aa0275a450942d7f113c0cb (diff)
perf/ring_buffer: Add ordering to rb->nest increment
commit 3f9fbe9bd86c534eba2faf5d840fd44c6049f50e upstream. 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> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 31edf1f39cca..d32b9375ec0e 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -49,6 +49,15 @@ static void perf_output_put_handle(struct perf_output_handle *handle)
unsigned long head;
+ /*
+ * 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);