linux-kernel - Re: [rfcomm_run] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156 __might

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Date:	Thu, 2 Oct 2014 21:11:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Jet Chen <jet.chen@...el.com>, Su Tao <tao.su@...el.com>,
	Yuanhan Liu <yuanhan.liu@...el.com>, LKP <lkp@...org>,
	linux-kernel@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [rfcomm_run] WARNING: CPU: 1 PID: 79 at
	kernel/sched/core.c:7156 __might_sleep()

On 10/02, Peter Zijlstra wrote:
>
> On Thu, Oct 02, 2014 at 03:52:50PM +0200, Peter Zijlstra wrote:
> > > If yes, then wakeups from signals don't work either, right?
> >
> > Its a kthread, there should not be any signals.
>
> That said, in the tty patch we do appear to have this problem.
>
> Oleg, do we want something like the below on top to make that work
> again?
>
> ---
> --- a/kernel/sched/wait.c
> +++ b/kernel/sched/wait.c
> @@ -326,8 +326,10 @@ long wait_woken(wait_queue_t *wait, unsi
>  	 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
>  	 * also observe all state before the wakeup.
>  	 */
> -	if (!(wait->flags & WQ_FLAG_WOKEN))
> -		timeout = schedule_timeout(timeout);
> +	if (!(wait->flags & WQ_FLAG_WOKEN)) {
> +		if (___wait_is_interruptible(mode) && !signal_pending_state(mode, current))
> +			timeout = schedule_timeout(timeout);
> +	}
>  	__set_current_state(TASK_RUNNING);

I am a bit confused... but for what?

schedule() won't sleep if signal_pending_state(mode) anyway, so we
do not need this correctness-wise. And the caller needs to check
signal_pending() anyway.

We can probably add

	if (signal_pending_state(mode, current))
		return -EINTR;

at the start of wait_woken(), even before set_current_state(mode).
Then the caller can check "ret < 0" and avoid signal_pending().
Not sure this makes sense.

Oleg.

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