linux-kernel - Re: WARN_ON_ONCE() hit at kernel/events/core.c:330

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Date:   Wed, 10 Apr 2019 16:33:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas-Mich Richter <tmricht@...ux.ibm.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>, acme@...hat.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Hendrik Brueckner <brueckner@...ux.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>, jolsa@...hat.com,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: WARN_ON_ONCE() hit at kernel/events/core.c:330

On Wed, Apr 10, 2019 at 03:51:24PM +0200, Thomas-Mich Richter wrote:
> Thanks for the fix with commit id 86071b11317550d994b55ce5e31aa06bcad783b5.
> 
> However doing an fgrep on the pending_disable member of struct perf_event
> reveals two more hits in file kernel/events/ringbuffer.c when events
> have auxiliary data.
> 
> Not sure if this needs to be addresses too, just wanted to let you know.

*groan* indeed, and yes that would need fixing too. I completely missed
the AUX stuff using that too.

I think we can simply do the below on top, Alexander?

---
 kernel/events/ring_buffer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 678ccec60d8f..ab2b7b38adc5 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -392,7 +392,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
 		 * store that will be enabled on successful return
 		 */
 		if (!handle->size) { /* A, matches D */
-			event->pending_disable = 1;
+			event->pending_disable = smp_processor_id();
 			perf_output_wakeup(handle);
 			local_set(&rb->aux_nest, 0);
 			goto err_put;
@@ -480,7 +480,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)

 	if (wakeup) {
 		if (handle->aux_flags & PERF_AUX_FLAG_TRUNCATED)
-			handle->event->pending_disable = 1;
+			handle->event->pending_disable = smp_processor_id();
 		perf_output_wakeup(handle);
 	}