linux-kernel - [PATCH 1/1] timer: Warn about schedule_timeout() called for tasks in TASK

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Date:   Thu, 16 Jan 2020 17:02:18 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Cc:     notify@...nel.org
Subject: [PATCH 1/1] timer: Warn about schedule_timeout() called for tasks in TASK_RUNNING state

When we were preparing the patch 6dcd5d7a7a29c1e, we made a mistake noticed
by Linus: schedule_timeout() was called without setting the task state to
anything particular. It calls the scheduler, but doesn't delay anything,
because the task stays runnable. That happens because sched_submit_work()
does nothing for tasks in TASK_RUNNING state.

Let's add a WARN_ONCE() under CONFIG_SCHED_DEBUG to detect such kernel
API misuse.

Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
 kernel/time/timer.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 4820823515e9..52ad2d6ce352 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1887,6 +1887,11 @@ signed long __sched schedule_timeout(signed long timeout)
 		}
 	}
 
+#ifdef CONFIG_SCHED_DEBUG
+	WARN_ONCE(current->state == TASK_RUNNING,
+			"schedule_timeout for TASK_RUNNING\n");
+#endif
+
 	expire = timeout + jiffies;
 
 	timer.task = current;
-- 
2.24.1