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 21:18:46 +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()

Ah, somehow I missed this email, I already replied to the previous one.

On 10/02, Peter Zijlstra wrote:
>
> In any case, if we change wait_woken() like the below, then we can
> simplify the loops by taking out their signal_pending checks and using
> the wait_woken() return value instead.

Yes, but let me repeat,

> +++ b/kernel/sched/wait.c
> @@ -326,8 +326,14 @@ 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)) {

___wait_is_interruptible() is pointless, signal_pending_state() does
the same checks. Not to mention it will always return T in this case,
note that __builtin_constant_p(state) == F.


> +		       if (signal_pending_state(mode, current))
> +			       timeout = -ERESTARTSYS;

OK, but unless I missed something this looks overcomplicated. You can
simply do this at the start of wait_woken(). Not need to play with
current->state, no need to clear WQ_FLAG_WOKEN.

Oleg.

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