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Subject: Re: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking
From: Arjan van de Ven <arjan@linux.intel.com>
To: Jens Axboe <axboe@suse.de>
Cc: Laurent Riffard <laurent.riffard@free.fr>,
       Kernel development list <linux-kernel@vger.kernel.org>,
       petero2@telia.com
In-Reply-To: <20060612164152.GP4420@suse.de>
References: <448875D1.5080905@free.fr> <448D84C0.1070400@linux.intel.com>
	 <20060612164152.GP4420@suse.de>
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Date: Wed, 21 Jun 2006 12:21:15 +0200
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On Mon, 2006-06-12 at 18:41 +0200, Jens Axboe wrote:
> On Mon, Jun 12 2006, Arjan van de Ven wrote:
> > Laurent Riffard wrote:
> > >Hello,
> > >
> > >This BUG happened while pktcdvd service was starting. 
> > >Basically, the 2 following commands were issued:
> > >- modprobe ptkcdvd
> > >- pktsetup dvd /dev/dvd
> > 
> > This appears to be a real bug:
> > 
> > A normal pkt dvd block dev open takes the
> > bdev_mutex in the regular block device open path, which takes
> > ctl_mutex in the pkt_open function which gets called then from
> > the block layer.
> > 
> > HOWEVER the IOCTL path does it the other way around:
> > 
> >                 mutex_lock(&ctl_mutex);
> >                 ret = pkt_setup_dev(&ctrl_cmd);
> >                 mutex_unlock(&ctl_mutex);
> > 
> > where pkt_setup_dev in term calls pkt_new_dev which
> > calls blkdev_get(), which takes the bdev_mutex.
> > 
> > Looks very much like a AB-BA deadlock to me...
> 
> I'd say you are right, however I haven't touched that code since 2.5 I
> think - CC'ing Peter for a fix!

ping ?