linux-kernel - [tip:perf/core] perf/core: Disable the event on a truncated AUX record

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Date:	Thu, 12 May 2016 03:35:01 -0700
From:	tip-bot for Alexander Shishkin <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	peterz@...radead.org, jolsa@...hat.com,
	torvalds@...ux-foundation.org, acme@...radead.org,
	markus.t.metzger@...el.com, alexander.shishkin@...ux.intel.com,
	bp@...en8.de, linux-kernel@...r.kernel.org,
	vincent.weaver@...ne.edu, tglx@...utronix.de, mingo@...nel.org,
	eranian@...gle.com, acme@...hat.com, hpa@...or.com
Subject: [tip:perf/core] perf/core: Disable the event on a truncated AUX
 record

Commit-ID:  3f56e687a138481894a1088d5aa7d41951bdb020
Gitweb:     http://git.kernel.org/tip/3f56e687a138481894a1088d5aa7d41951bdb020
Author:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
AuthorDate: Tue, 10 May 2016 16:18:33 +0300
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 12 May 2016 10:14:55 +0200

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

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.

Reported-by: Markus Metzger <markus.t.metzger@...el.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Arnaldo Carvalho de Melo <acme@...radead.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: vince@...ter.net
Link: http://lkml.kernel.org/r/1462886313-13660-3-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/ring_buffer.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index c49bab4..ae9b90d 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -405,6 +405,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
 			 bool truncated)
 {
 	struct ring_buffer *rb = handle->rb;
+	bool wakeup = truncated;
 	unsigned long aux_head;
 	u64 flags = 0;
 
@@ -433,9 +434,16 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
 	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);