From: Arjan van de Ven <arjan@linux.intel.com>
To: Peter Osterlund <petero2@telia.com>
Cc: Laurent Riffard <laurent.riffard@free.fr>,
Kernel development list <linux-kernel@vger.kernel.org>,
axboe@suse.de
Subject: Re: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking
Date: Fri, 14 Jul 2006 15:46:10 +0200 [thread overview]
Message-ID: <1152884770.3159.37.camel@laptopd505.fenrus.org> (raw)
In-Reply-To: <m3u05kqvla.fsf@telia.com>
On Fri, 2006-07-14 at 13:22 +0200, Peter Osterlund wrote:
> > and what locking prevents this? And via multiple opens?
>
> You are right that my reasoning was incorrect. If someone is doing
> "pktsetup ; pktsetup -d" quickly in a loop while someone else is
> trying to open the device, one thread could be at the start of
> pkt_open() at the same time as another thread is in pkt_new_dev().
>
> However, I added a 5s delay in pkt_open() to enlarge the race window.
> I still couldn't make the driver lock up though. The explanation is
> that pkt_new_dev() calls blkdev_get() with the CD device (eg /dev/hdc)
> as bdev parameter, while do_open() locks the bd_mutex for the pktcdvd
> device (eg /dev/pktcdvd/0).
>
> Do you still think this could deadlock? If not, how should the code be
> annotated to make this warning go away?
unless we KNOW it won't deadlock (eg we have a "this cannot deadlock
BECAUSE of X, Y and Z") I don't think annotations are the right idea. In
addition, the "how to annotate" really depends on what X, Y and Z
are....
next prev parent reply other threads:[~2006-07-14 13:46 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-06-08 19:09 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking Laurent Riffard
2006-06-12 15:14 ` Arjan van de Ven
2006-06-12 16:41 ` Jens Axboe
2006-06-21 10:21 ` Arjan van de Ven
2006-06-22 14:50 ` Peter Osterlund
2006-06-22 18:20 ` Arjan van de Ven
2006-07-14 11:22 ` Peter Osterlund
2006-07-14 13:46 ` Arjan van de Ven [this message]
2006-07-14 21:06 ` Peter Osterlund
2006-07-14 22:29 ` Arjan van de Ven
2006-07-15 7:04 ` [patch] lockdep: annotate pktcdvd natural device hierarchy Arjan van de Ven
2006-07-15 10:35 ` Laurent Riffard
2006-07-15 10:57 ` Peter Osterlund
2006-07-16 10:33 ` Laurent Riffard
2006-07-25 2:27 ` Andrew Morton
2006-07-25 5:34 ` Arjan van de Ven
2006-07-25 6:31 ` Andrew Morton
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