perf, x86: Fix LBR enable/disable vs cpuc->enabled

We should never call ->enable with the pmu enabled, and we _can_ have
->disable called with the pmu enabled.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: paulus@samba.org
Cc: eranian@google.com
Cc: robert.richter@amd.com
Cc: fweisbec@gmail.com
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/perf_event_intel_lbr.c

@@ -69,7 +69,7 @@ static void intel_pmu_lbr_enable(struct perf_event *event)
 	if (!x86_pmu.lbr_nr)
 		return;
 
-	WARN_ON(cpuc->enabled);
+	WARN_ON_ONCE(cpuc->enabled);
 
 	/*
 	 * Reset the LBR stack if this is the first LBR user or
@@ -93,9 +93,10 @@ static void intel_pmu_lbr_disable(struct perf_event *event)
 		return;
 
 	cpuc->lbr_users--;
-
 	BUG_ON(cpuc->lbr_users < 0);
-	WARN_ON(cpuc->enabled);
+
+	if (cpuc->enabled && !cpuc->lbr_users)
+		__intel_pmu_lbr_disable();
 }
 
 static void intel_pmu_lbr_enable_all(void)