Re: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking

[Arjan van de Ven <arjan@linux.intel.com>]

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...

Jens?