perf: Fix PERF_EVENT_IOC_PERIOD deadlock

commit 642c2d67 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@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: c7999c6f ("perf: Fix PERF_EVENT_IOC_PERIOD migration race")
Link: http://lkml.kernel.org/r/20151130115615.GJ17308@twins.programming.kicks-ass.netSigned-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

kernel/events/core.c

@@ -3692,7 +3692,14 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
 		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;