perf_events, x86: Fix validate_event bug

The validate_event() was failing on valid event combinations. The
function was assuming that if x86_schedule_event() returned 0, it
meant error. But x86_schedule_event() returns the counter index and
0 is a perfectly valid value. An error is returned if the function
returns a negative value.

Furthermore, validate_event() was also failing for event groups
because the event->pmu was not set until after
hw_perf_event_init().
Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: peterz@infradead.org
Cc: paulus@samba.org
Cc: perfmon2-devel@lists.sourceforge.net
Cc: eranian@gmail.com
LKML-Reference: <4b0bdf36.1818d00a.07cc.25ae@mx.google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
--
 arch/x86/kernel/cpu/perf_event.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

arch/x86/kernel/cpu/perf_event.c

@@ -2229,10 +2229,10 @@ validate_event(struct cpu_hw_events *cpuc, struct perf_event *event)
 {
 	struct hw_perf_event fake_event = event->hw;
 
-	if (event->pmu != &pmu)
+	if (event->pmu && event->pmu != &pmu)
 		return 0;
 
-	return x86_schedule_event(cpuc, &fake_event);
+	return x86_schedule_event(cpuc, &fake_event) >= 0;
 }
 
 static int validate_group(struct perf_event *event)