tracing: Fix return value check in trace_benchmark_reg()

In case of error, the function kthread_run() returns ERR_PTR() and never
returns NULL. The NULL test in the return value check should be replaced
with IS_ERR().

Link: http://lkml.kernel.org/r/20170112135502.28556-1-weiyj.lk@gmail.com

Cc: stable@vger.kernel.org
Fixes: 81dc9f0e ("tracing: Add tracepoint benchmark tracepoint")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_benchmark.c

@@ -175,9 +175,9 @@ int trace_benchmark_reg(void)
 
 	bm_event_thread = kthread_run(benchmark_event_kthread,
 				      NULL, "event_benchmark");
-	if (!bm_event_thread) {
+	if (IS_ERR(bm_event_thread)) {
 		pr_warning("trace benchmark failed to create kernel thread\n");
-		return -ENOMEM;
+		return PTR_ERR(bm_event_thread);
 	}
 
 	return 0;