[PATCH 4.2.y-ckt 144/305] perf: Fix PERF_EVENT_IOC_PERIOD deadlock

[Kamal Mostafa]

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

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

From: Peter Zijlstra <peterz at infradead.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 at google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Cc: Alexander Potapenko <glider at google.com>
Cc: Arnaldo Carvalho de Melo <acme at kernel.org>
Cc: Arnaldo Carvalho de Melo <acme at redhat.com>
Cc: Eric Dumazet <edumazet at google.com>
Cc: Jiri Olsa <jolsa at redhat.com>
Cc: Kostya Serebryany <kcc at google.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Sasha Levin <sasha.levin at oracle.com>
Cc: Stephane Eranian <eranian at google.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Vince Weaver <vincent.weaver at maine.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 at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.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