Messages in this thread | | | Subject | Re: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking | From | Arjan van de Ven <> | Date | Thu, 22 Jun 2006 20:20:51 +0200 |
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On Thu, 2006-06-22 at 16:50 +0200, Peter Osterlund wrote: > Arjan van de Ven <arjan@linux.intel.com> writes: > > > 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 don't understand how this could deadlock. If the device is already > setup, pkt_new_dev() returns before calling blkdev_get(). If the > device is not already setup, the block device doesn't exist yet so > there can not be another caller in the pkt_open() path.
and what locking prevents this? And via multiple opens?
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