Patch "perf/core: Disable the event on a truncated AUX record" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

perf/core: Disable the event on a truncated AUX record

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-core-disable-the-event-on-a-truncated-aux-record.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexander Shishkin <[email protected]>
Date: Tue, 10 May 2016 16:18:33 +0300
Subject: perf/core: Disable the event on a truncated AUX record

From: Alexander Shishkin <[email protected]>

commit 9f448cd3cbcec8995935e60b27802ae56aac8cc0 upstream.

When the PMU driver reports a truncated AUX record, it effectively means that there is no more usable room in the event's AUX buffer (even though there may still be some room, so that perf_aux_output_begin() doesn't take action). At this point the consumer still has to be woken up and the event has to be disabled, otherwise the event will just keep spinning between perf_aux_output_begin() and perf_aux_output_end() until its context gets unscheduled.

Again, for cpu-wide events this means never, so once in this condition, they will be forever losing data.

Fix this by disabling the event and waking up the consumer in case of a truncated AUX record.

---
 kernel/events/ring_buffer.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

@@ -347,6 +347,7 @@ void perf_aux_output_end(struct perf_out
 			 bool truncated)
 {
 	struct ring_buffer *rb = handle->rb;
+	bool wakeup = truncated;
 	unsigned long aux_head;
 	u64 flags = 0;
 

@@ -375,9 +376,16 @@ void perf_aux_output_end(struct perf_out
 	aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
 
 	if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
-		perf_output_wakeup(handle);
+		wakeup = true;
 		local_add(rb->aux_watermark, &rb->aux_wakeup);
 	}
+
+	if (wakeup) {
+		if (truncated)
+			handle->event->pending_disable = 1;
+		perf_output_wakeup(handle);
+	}
+
 	handle->event = NULL;
 
 	local_set(&rb->aux_nest, 0);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/perf-core-disable-the-event-on-a-truncated-aux-record.patch