linux-kernel - [tip:perf/urgent] perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user

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Date:   Fri, 24 May 2019 01:09:36 -0700
From:   tip-bot for Peter Zijlstra <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     alexander.shishkin@...ux.intel.com, eranian@...gle.com,
        tglx@...utronix.de, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, jolsa@...hat.com,
        vincent.weaver@...ne.edu, yabinc@...gle.com, acme@...hat.com,
        mingo@...nel.org, hpa@...or.com, peterz@...radead.org
Subject: [tip:perf/urgent] perf/ring-buffer: Always use {READ,WRITE}_ONCE()
 for rb->user_page data

Commit-ID:  4d839dd9e4356bbacf3eb0ab13a549b83b008c21
Gitweb:     https://git.kernel.org/tip/4d839dd9e4356bbacf3eb0ab13a549b83b008c21
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Fri, 17 May 2019 13:52:33 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 24 May 2019 09:00:11 +0200

perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data

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@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: acme@...nel.org
Cc: mark.rutland@....com
Cc: namhyung@...nel.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@...nel.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 4b5f8d932400..7a0c73e4b3eb 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -100,7 +100,7 @@ again:
 	 * 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,
@@ -496,7 +496,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
 		perf_event_aux_event(handle->event, aux_head, 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;
 
@@ -528,7 +528,7 @@ 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;