linux-kernel - [PATCH 4.2.y-ckt 144/305] perf: Fix PERF_EVENT_IOC

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Message-Id: <1452902519-2754-145-git-send-email-kamal@canonical.com>
Date:	Fri, 15 Jan 2016 15:59:18 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Alexander Potapenko <glider@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Stephane Eranian <eranian@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Ingo Molnar <mingo@...nel.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 144/305] perf: Fix PERF_EVENT_IOC_PERIOD deadlock

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Peter Zijlstra <peterz@...radead.org>

commit 642c2d671ceff40e9453203ea0c66e991e11e249 upstream.

Dmitry reported a fairly silly recursive lock deadlock for
PERF_EVENT_IOC_PERIOD, fix this by explicitly doing the inactive part of
__perf_event_period() instead of calling that function.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Kostya Serebryany <kcc@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sasha Levin <sasha.levin@...cle.com>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Fixes: c7999c6f3fed ("perf: Fix PERF_EVENT_IOC_PERIOD migration race")
Link: http://lkml.kernel.org/r/20151130115615.GJ17308@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 kernel/events/core.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index c06fa66..d86859f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4034,7 +4034,14 @@ retry:
 		goto retry;
 	}
 
-	__perf_event_period(&pe);
+	if (event->attr.freq) {
+		event->attr.sample_freq = value;
+	} else {
+		event->attr.sample_period = value;
+		event->hw.sample_period = value;
+	}
+
+	local64_set(&event->hw.period_left, 0);
 	raw_spin_unlock_irq(&ctx->lock);
 
 	return 0;
-- 
1.9.1