linux-kernel - Re: [PATCH] fix-flush_workqueue-vs-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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Tue, 9 Jan 2007 17:38:23 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	Andrew Morton <akpm@...l.org>, David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel@...r.kernel.org, Gautham shenoy <ego@...ibm.com>
Subject: Re: [PATCH] fix-flush_workqueue-vs-cpu_dead-race-update

On 01/09, Srivatsa Vaddagiri wrote:
>
> On Mon, Jan 08, 2007 at 08:06:35PM +0300, Oleg Nesterov wrote:
> > Ah, missed you point, thanks. Yet another old problem which was not introduced
> > by recent changes. And yet another indication we should avoid kthread_stop()
> > on CPU_DEAD event :) I believe this is easy to fix, but need to think more.
> 
> I think the problem is not just with CPU_DEAD. Anyone who calls
> cleanup_workqueue_thread (say destroy_workqueue?) will see this race. 

destroy_workqueue() first does flush_workqueue(), so it should be ok.

Anyway I agree with you, we shouldn't clear cwq->thread until it exits,

> Do you see any problems if cleanup_workqueue_thread is changed as:
> 
> cleanup_workqueue_thread()
> {
> 	kthread_stop(p);
> 	spin_lock(cwq->lock);
> 	cwq->thread = NULL;
> 	spin_unlock(cwq->lock);
> }

I think the same. In fact I suspect we even don't need spin_lock, but didn't
have a time to read the code since our discussion.

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/