perf: Really fix event_function_call() locking

Commit 558abc7 ("perf: Fix event_function_call() locking") lost
IRQ disabling by mistake.

Fixes: 558abc7 ("perf: Fix event_function_call() locking")
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Author: namhyung

kernel/events/core.c

@@ -298,8 +298,8 @@ static int event_function(void *info)
 static void event_function_call(struct perf_event *event, event_f func, void *data)
 {
 	struct perf_event_context *ctx = event->ctx;
-	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
 	struct task_struct *task = READ_ONCE(ctx->task); /* verified in event_function */
+	struct perf_cpu_context *cpuctx;
 	struct event_function_struct efs = {
 		.event = event,
 		.func = func,
@@ -327,22 +327,25 @@ static void event_function_call(struct perf_event *event, event_f func, void *da
 	if (!task_function_call(task, event_function, &efs))
 		return;
 
+	local_irq_disable();
+	cpuctx = this_cpu_ptr(&perf_cpu_context);
 	perf_ctx_lock(cpuctx, ctx);
 	/*
 	 * Reload the task pointer, it might have been changed by
 	 * a concurrent perf_event_context_sched_out().
 	 */
 	task = ctx->task;
-	if (task == TASK_TOMBSTONE) {
-		perf_ctx_unlock(cpuctx, ctx);
-		return;
-	}
+	if (task == TASK_TOMBSTONE)
+		goto unlock;
 	if (ctx->is_active) {
 		perf_ctx_unlock(cpuctx, ctx);
+		local_irq_enable();
 		goto again;
 	}
 	func(event, NULL, ctx, data);
+unlock:
 	perf_ctx_unlock(cpuctx, ctx);
+	local_irq_enable();
 }
 
 /*