Commit 991ea848 authored May 17, 2019 by Peter Zijlstra Committed by Greg Kroah-Hartman Jun 22, 2019

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



[ 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: 7b732a75 ("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>

parent c133c9db

kernel/events/ring_buffer.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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;