linux-kernel - Re: 2.6.21-rc7-mm1: BUG_ON in kthread_bind during _cpu

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 for Android: free password hash cracker in your pocket

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

Date:	Thu, 26 Apr 2007 14:15:47 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-rc7-mm1: BUG_ON in kthread_bind during _cpu_down

On 04/26, Gautham R Shenoy wrote:
>
> On Wed, Apr 25, 2007 at 04:54:10PM -0700, Andrew Morton wrote:
> > On Thu, 26 Apr 2007 01:10:21 +0200 "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> > 
> > > Hi,
> > > 
> > > The BUG_ON in khthread_bind (line 165 in kthread.c) triggers for me during
> > > attempted suspend to disk, when disable_nonboot_cpus() calls _cpu_down()
> > > (on x86_64).
> > 
> Caused due to Oleg's patch http://lkml.org/lkml/2007/4/13/93.
> 
> Agreed that most of the time a kthread_create(p) is followed by a
> kthread_bind(p), in which case the assertion 
> WARN_ON(p->state != TASK_UNINTERRUPTIBLE) makes sense.
> 
> But, in cpu hotplug case, we need to rebind the stop_machine_run thread
> from the cpu which has just been offlined to any online cpu.
> (kernel/cpu.c line 180)

I can't understand why do we need to re-bind this thread. We are doing
kthread_stop()->wake_up() below, at this point move_task_off_dead_cpu()
has already cared about this task, no?

> We only need to ensure in kthread_bind that the task which is being
> bound is not running or exiting. Doesn't matter if it's sleeping in 
> TASK_INTERRUPTIBLE or TASK_UNINTERRUPTIBLE state.

We need to ensure that this task can't be woken after return from
wait_task_inactive(k), otherwise set_task_cpu() after that is not safe.

TASK_INTERRUPTIBLE doesn't protect us from freezing.

Couldn't we just remove this kthread_bind() ?

Oleg.

-
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/