[PATCH AUTOSEL 4.19 15/49] perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data

Sasha Levin
2019-06-08T11:45:25Z

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit 4d839dd9e4356bbacf3eb0ab13a549b83b008c21 ]

We must use {READ,WRITE}_ONCE() on rb->user_page data such that
concurrent usage will see whole values. A few key sites were missing
this.

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: 7b732a750477 ("perf_counter: new output ABI - part 1")
Link: http://lkml.kernel.org/r/20190517115418.394192145@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/events/ring_buffer.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index d32b9375ec0e..12f351b253bb 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -101,7 +101,7 @@ static void perf_output_put_handle(struct perf_output_handle *handle)
* See perf_output_begin().
*/
smp_wmb(); /* B, matches C */
- rb->user_page->data_head = head;
+ WRITE_ONCE(rb->user_page->data_head, head);

/*
* We must publish the head before decrementing the nest count,
@@ -490,7 +490,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
handle->aux_flags);
}

- rb->user_page->aux_head = rb->aux_head;
+ WRITE_ONCE(rb->user_page->aux_head, rb->aux_head);
if (rb_need_aux_wakeup(rb))
wakeup = true;

@@ -522,7 +522,7 @@ int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)

rb->aux_head += size;

- rb->user_page->aux_head = rb->aux_head;
+ WRITE_ONCE(rb->user_page->aux_head, rb->aux_head);
if (rb_need_aux_wakeup(rb)) {
perf_output_wakeup(handle);
handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
--
2.20.1