ring_buffer: Allow to exit the ring buffer benchmark immediately

It takes a while until the ring_buffer_benchmark module is removed
when the ring buffer hammer is running. It is because it takes
few seconds and kthread_should_stop() is not being checked.

This patch adds the check for kthread termination into the producer.
It uses the existing @kill_test flag to finish the kthreads as
cleanly as possible.

It disables printing the "ERROR" message when the kthread is going.

It makes sure that producer does not go into the 10sec sleep
when it is being killed.

Finally, it does not call wait_to_die() when kthread_should_stop()
already returns true.

Link: http://lkml.kernel.org/r/20150615155428.GD3135@pathway.suse.cz

Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ring_buffer_benchmark.c

@@ -263,6 +263,8 @@ static void ring_buffer_producer(void)
 		if (cnt % wakeup_interval)
 			cond_resched();
 #endif
+		if (kthread_should_stop())
+			kill_test = 1;
 
 	} while (ktime_before(end_time, timeout) && !kill_test);
 	trace_printk("End ring buffer hammer\n");
@@ -285,7 +287,7 @@ static void ring_buffer_producer(void)
 	entries = ring_buffer_entries(buffer);
 	overruns = ring_buffer_overruns(buffer);
 
-	if (kill_test)
+	if (kill_test && !kthread_should_stop())
 		trace_printk("ERROR!\n");
 
 	if (!disable_reader) {
@@ -379,7 +381,7 @@ static int ring_buffer_consumer_thread(void *arg)
 	}
 	__set_current_state(TASK_RUNNING);
 
-	if (kill_test)
+	if (!kthread_should_stop())
 		wait_to_die();
 
 	return 0;
@@ -399,13 +401,16 @@ static int ring_buffer_producer_thread(void *arg)
 		}
 
 		ring_buffer_producer();
+		if (kill_test)
+			goto out_kill;
 
 		trace_printk("Sleeping for 10 secs\n");
 		set_current_state(TASK_INTERRUPTIBLE);
 		schedule_timeout(HZ * SLEEP_TIME);
 	}
 
-	if (kill_test)
+out_kill:
+	if (!kthread_should_stop())
 		wait_to_die();
 
 	return 0;