linux-kernel - Re: Problem with freezable workqueues

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:	Wed, 28 Feb 2007 08:37:26 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Oleg Nesterov <oleg@...sign.ru>, Pavel Machek <pavel@....cz>,
	Gautham R Shenoy <ego@...ibm.com>,
	Johannes Berg <johannes@...solutions.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem with freezable workqueues

On Wed, Feb 28, 2007 at 12:57:35AM +0100, Rafael J. Wysocki wrote:
> > How about other kthread_stop()s ? For example, kernel/softirq.c:cpu_callback() ?
> 
> They all are PF_NOFREEZE, I suppose.  If we make all workqueues nonfreezable
> (as they were before), the problem won't appear.

We can just thaw the worker thread selectively before kthread_stopping
them. This will let us freeze all worker threads (which we want to for
hotplug anyway).

> > I think we need a general "cpu_down() after freeze" implementation, this is what
> > Gautham and Srivatsa are working on, right?
> 
> Yes, certainly.

Hmm ..good point. So can we assume that disable/enable_nonboot_cpus() are called
with processes frozen already?

Gautham, you need to take this into account in your patchset!

> > I'm afraid this is racy. We can't touch *cwq, it may be freed. Suppose
> > that another thread does destroy_workqueue(), and we thaw that thread
> > before cwq->thread.
> 
> Okay, in that case I'd suggest removing create_freezeable_workqueue() and
> make all workqueues nonfreezable once again for 2.6.21 (as far as I know, only
> the two XFS workqueues are affected).

See above suggestion of thawing worker thread before kthread_stopping
it.

-- 
Regards,
vatsa
-
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/