Date: Tue, 16 Dec 2008 23:16:10 +0000 (UTC) From: Attilio Rao <attilio@FreeBSD.org> To: cvs-src-old@freebsd.org Subject: cvs commit: src/sys/kern vfs_mount.c vfs_subr.c src/sys/sys mount.h Message-ID: <200812162316.mBGNGgo5052957@repoman.freebsd.org>
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attilio 2008-12-16 23:16:10 UTC
FreeBSD src repository
Modified files:
sys/kern vfs_mount.c vfs_subr.c
sys/sys mount.h
Log:
SVN rev 186197 on 2008-12-16 23:16:10Z by attilio
1) Fix a deadlock in the VFS:
- threadA runs vfs_rel(mp1)
- threadB does unmount the mp1 fs, sets MNTK_UNMOUNT and drop MNT_ILOCK()
- threadA runs vfs_busy(mp1) and, as long as, MNTK_UNMOUNT is set, sleeps
waiting for threadB to complete the unmount
- threadB, in vfs_mount_destroy(), finds mnt_lock > 0 and sleeps waiting
for the refcount to expire.
Fix the deadlock by adding a flag called MNTK_REFEXPIRE which signals the
unmounter is waiting for mnt_ref to expire.
The vfs_busy contenders got awake, fails, and if they retry the
MNTK_REFEXPIRE won't allow them to sleep again.
2) Simplify significantly the code of vfs_mount_destroy() trimming
unnecessary codes:
- as long as any reference exited, it is no-more possible to have
write-op (primarty and secondary) in progress.
- it is no needed to drop and reacquire the mount lock.
- filling the structures with dummy values is unuseful as long as
it is going to be freed.
Tested by: pho, Andrea Barberio <insomniac at slackware dot it>
Discussed with: kib
Revision Changes Path
1.298 +14 -31 src/sys/kern/vfs_mount.c
1.750 +1 -1 src/sys/kern/vfs_subr.c
1.240 +1 -0 src/sys/sys/mount.h
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