linux-kernel - Re: [PATCH 1/2] workqueue: Catch more locking problems with flush

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:	Fri, 20 Apr 2012 15:18:00 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	netdev@...r.kernel.org, Ben Dooks <ben-linux@...ff.org>
Subject: Re: [PATCH 1/2] workqueue: Catch more locking problems with
 flush_work()

On Thu, Apr 19, 2012 at 11:26:47PM -0700, Stephen Boyd wrote:
> complain in the case where the work is not queued. That case is not a
> false positive. We will get a lockdep warning if the work is running

IIRC, flush_work() is just a nop when a work is not queued nor running.

> (when start_flush_work() returns true) solely with the
> lock_map_acquire() on cwq->wq->lockdep_map.

Yeah, that is the point we use lockdep to detect deadlock for workqueue.

But when looking at start_flush_work(), for some case
!(cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER),
lock_map_acquire_read() is called, but recursive read is not added to
the chain list. So when lock_map_acquire_read(&cwq->wq->lockdep_map)
is called, deadlock will not be detected. I hope you don't hit that
special case.

Thanks,
Yong
--
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/