On Wed, Apr 08, 2015 at 10:20:22PM +0800, Ming Lei wrote: > On Wed, Apr 8, 2015 at 10:00 PM, Jarod Wilson <jarod@xxxxxxxxxx> wrote: > > On Wed, Apr 08, 2015 at 09:40:34AM -0400, Jarod Wilson wrote: > >> 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 <jarod@xxxxxxxxxx> wrote: > >> > > From: Ming Lei <ming.lei@xxxxxxxxxxxxx> > >> > > > >> > > 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. > > > > Are you working on that atomic_t version then, or should I dive into it? > > It has been ready, and I will post them out once it passes my tests. Okay, I'll hold tight then. Sorry for the noise. :p -- Jarod Wilson jarod@xxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
