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.
Fixes:7b732a750477 ("perf_counter: new output ABI - part 1") Suggested-by: Yabin Cui <yab...@google.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> --- kernel/events/ring_buffer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -100,7 +100,7 @@ static void perf_output_put_handle(struc * 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_out 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_out 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;