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

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Date:	Sat, 4 Oct 2014 10:44:59 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	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>,
	Peter Hurley <peter@...leysoftware.com>
Subject: Re: [rfcomm_run] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156
 __might_sleep()

On Fri, Oct 03, 2014 at 07:56:54PM +0200, Oleg Nesterov wrote:
> Or. perhaps we can change wait_woken
> 
> 	-	set_current_state(mode);
> 	+	if (mode)
> 	+		set_current_state(mode);
> 
> 
> then rfcomm_run() can do
> 
> 	for (;;) {
> 		rfcomm_process_sessions();
> 
> 		set_current_state(TASK_INTERRUPTIBLE);
> 		if (kthread_should_stop())
> 			break;
> 		wait_woken(0);
> 	}
> 
> Or perhaps we can split wait_woken() into 2 helpers,
> 
> 	static inline long wait_woken(wq, mode, timeout)
> 	{
> 		set_current_state(mode);
> 		schedule_woken(wq, timeout); // does the rest
> 	}
> 
> to avoid "mode == 0" hack; rfcomm_run() should use schedule_woken().
> 
> What do you think?

Clever, I'm not entirely sure which I prefer, I think I'm leaning
towards the first one with the !mode hack, but let me sit on that for a
little while.
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