linux-kernel - [tip:perf/urgent] perf/core: Fix the unthrottle logic

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Date:	Mon, 21 Mar 2016 02:48:39 -0700
From:	tip-bot for Peter Zijlstra <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	mingo@...nel.org, dvlasenk@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, eranian@...gle.com,
	vincent.weaver@...ne.edu, peterz@...radead.org, brgerst@...il.com,
	acme@...hat.com, bp@...en8.de, dsahern@...il.com,
	tglx@...utronix.de, jolsa@...hat.com, luto@...capital.net,
	torvalds@...ux-foundation.org, namhyung@...nel.org,
	alexander.shishkin@...ux.intel.com
Subject: [tip:perf/urgent] perf/core: Fix the unthrottle logic

Commit-ID:  1e02cd40f15190b78fcc6b3f50c952fb4028e9a5
Gitweb:     http://git.kernel.org/tip/1e02cd40f15190b78fcc6b3f50c952fb4028e9a5
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 10 Mar 2016 15:39:24 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 21 Mar 2016 09:08:14 +0100

perf/core: Fix the unthrottle logic

Its possible to IOC_PERIOD while the event is throttled, this would
re-start the event and the next tick would then try to unthrottle it,
and find the event wasn't actually stopped anymore.

This would tickle a WARN in the x86-pmu code which isn't expecting to
start a !stopped event.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David Ahern <dsahern@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Namhyung Kim <namhyung@...nel.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: dvyukov@...gle.com
Cc: oleg@...hat.com
Cc: panand@...hat.com
Cc: sasha.levin@...cle.com
Cc: vince@...ter.net
Link: http://lkml.kernel.org/r/20160310143924.GR6356@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 712570d..d394773 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4210,6 +4210,14 @@ static void __perf_event_period(struct perf_event *event,
 	active = (event->state == PERF_EVENT_STATE_ACTIVE);
 	if (active) {
 		perf_pmu_disable(ctx->pmu);
+		/*
+		 * We could be throttled; unthrottle now to avoid the tick
+		 * trying to unthrottle while we already re-started the event.
+		 */
+		if (event->hw.interrupts == MAX_INTERRUPTS) {
+			event->hw.interrupts = 0;
+			perf_log_throttle(event, 1);
+		}
 		event->pmu->stop(event, PERF_EF_UPDATE);
 	}