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SubjectRe: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking
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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!

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