[PATCH] perf: do not set task_ctx pointer in cpuctx if there is no events in the context

[Gleb Natapov <gleb@redhat.com>]

Do not set task_ctx pointer during sched_in if there is no
events associated with the context.  Otherwise if during task
execution total number of events in the system will become zero
perf_event_context_sched_out() will not be called and cpuctx->task_ctx
will be left with a stale value.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0f85778..68b13ee 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2172,7 +2172,8 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
 
 	perf_event_sched_in(cpuctx, ctx, task);
 
-	cpuctx->task_ctx = ctx;
+	if (ctx->nr_events)
+		cpuctx->task_ctx = ctx;
 
 	perf_pmu_enable(ctx->pmu);
 	perf_ctx_unlock(cpuctx, ctx);
--
			Gleb.