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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 2 Oct 2014 14:42:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	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>, oleg@...hat.com
Subject: Re: [rfcomm_run] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156
 __might_sleep()

On Thu, Oct 02, 2014 at 02:31:50PM +0200, Peter Zijlstra wrote:
> @@ -2086,24 +2086,22 @@ static void rfcomm_kill_listener(void)
>  
>  static int rfcomm_run(void *unused)
>  {
> +	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>  	BT_DBG("");
>  
>  	set_user_nice(current, -10);
>  
>  	rfcomm_add_listener(BDADDR_ANY);
>  
> -	while (1) {
> -		set_current_state(TASK_INTERRUPTIBLE);
> -
> -		if (kthread_should_stop())
> -			break;
> +	add_wait_queue(&rfcomm_wq, &wait);
> +	while (!kthread_should_stop()) {
>  
>  		/* Process stuff */
>  		rfcomm_process_sessions();
>  
> -		schedule();
> +		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
>  	}
> -	__set_current_state(TASK_RUNNING);
> +	remove_wait_queue(&rfcomm_wq, &wait);
>  
>  	rfcomm_kill_listener();
>  

Hmm, I think there's a problem there. If someone were to do
kthread_stop() before wait_woken() we'd not actually stop, because
wait_woken() doesn't test KTHREAD_SHOULD_STOP before calling schedule().

We can't unconditionally put a kthread_should_stop() in because
to_kthread() would explode on a !kthread. The other obvious solution is
adding a second function, something like wait_woken_or_stop(), but that
appears somewhat ugly to me.

Oleg, do you see another solution?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/