linux-kernel - Re: [PATCH 7/7] sched: Use WARN_ONCE for the might_sleep() TASK

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Date:	Fri, 31 Oct 2014 23:42:37 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	peter@...leysoftware.com, rjw@...ysocki.net,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	eparis@...hat.com, umgwanakikbuti@...il.com, marcel@...tmann.org,
	ebiederm@...ssion.com, davem@...emloft.net, fengguang.wu@...el.com
Subject: Re: [PATCH 7/7] sched: Use WARN_ONCE for the might_sleep()
	TASK_RUNNING test

On 10/31, Peter Zijlstra wrote:
>
> In some cases this can trigger a true flood of output.
>
> Requested-by: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7301,7 +7301,7 @@ void __might_sleep(const char *file, int
>  	 * since we will exit with TASK_RUNNING make sure we enter with it,
>  	 * otherwise we will destroy state.
>  	 */
> -	if (WARN(current->state != TASK_RUNNING,
> +	if (WARN_ONCE(current->state != TASK_RUNNING,

Agreed, but sorry for off-topic, can't resist.

Sometimes I hate WARN_ONCE() because you can't reproduce the problem
once again without reboot.

Perhaps WARN_ON_RATELIMIT() should be used more often (not sure about
this particular case). Or, perhaps, we can add a special section for
these "__warned" variables and add, say, sysctl which clears that
section ?

Oleg.

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