On Wed, Apr 08, 2015 at 02:50:59PM +0800, Ming Lei wrote: > Hi Jarod, > > On Wed, Apr 8, 2015 at 2:23 PM, Jarod Wilson <ja...@redhat.com> wrote: > > From: Ming Lei <ming....@canonical.com> > > > > The lo_ctl_mutex is held for running all ioctl handlers, and > > in some ioctl handlers, ioctl_by_bdev(BLKRRPART) is called for > > rereading partitions, which requires bd_mutex. > > > > So it is easy to cause failure because trylock(bd_mutex) may > > fail inside blkdev_reread_part(), and follows the lock context: > > > > blkid or other application: > > ->open() > > ->mutex_lock(bd_mutex) > > ->lo_open() > > ->mutex_lock(lo_ctl_mutex) > > > > losetup(set fd ioctl): > > ->mutex_lock(lo_ctl_mutex) > > ->ioctl_by_bdev(BLKRRPART) > > ->trylock(bd_mutex) > > > > This patch trys to eliminate the ABBA lock dependency by removing > > lo_ctl_mutext in lo_open() with the following approach: > > > > 1) introduce lo_open_mutex to protect lo_refcnt and avoid acquiring > > lo_ctl_mutex in lo_open(): > > It is a bit quick since I said the lo_open_mutex can be removed, > and Christoph agreed that too. > > So looks we still need to post another version, :-)
Ah. I missed that bit. Just trying to keep up momentum. -- Jarod Wilson ja...@redhat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
