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    Subject[PATCH 4.19 29/61] perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data
    Date
    [ 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


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