On Mon, Jun 11, 2012 at 10:19:07AM -0700, Steven Haber wrote: > Hey FreeBSD devs, > > I hope this is the right forum for this. I haven't used the FreeBSD > mailing lists before. I'm a relatively new hire at EMC Isilon. We are > using FreeBSD 7.0 as the basis for our scale-out NAS product line. We > are frequently hitting the deadlock described here: > > http://lists.freebsd.org/pipermail/freebsd-geom/2010-February/003888.htm > l > > The race is that destroy_dev() sleeps indefinitely waiting for thread > references to drop from a dev. In the case of geom, we hold the topology > lock the whole time we're in the dev layer. In devfs_open() and > devfs_close(), we take a ref on the dev before calling into to geom. > > The proposed solution of destroy_dev_sched() makes sense to me. I am > trying to understand the necessity of Alexander Motin's additional > changes. destroy_dev_tq() holds the devmtx during the destroy and devfs > uses this lock to take refs before calling into geom. To me it seems we > should be able to protect the cdev with just the devmtx, provided > consumers of d_close(), d_open(), etc. ref and rel the dev > appropriately. devmtx is mutex. If taken, then cdevsw methods would be unable to sleep.
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