fsck_ufs locked in snaplk

[Pawel Jakub Dawidek]

On Wed, Apr 26, 2006 at 04:36:17PM +0300, Kostik Belousov wrote:
+> On Wed, Apr 26, 2006 at 01:43:42PM +0400, Dmitry Morozovsky wrote:
+> > On Tue, 25 Apr 2006, Kris Kennaway wrote:
+> > 
+> > KK> What people are seeing now must be some other problem that I wan't
+> > KK> able to reproduce.
+> > KK> 
+> > KK> Once I hear back from someone who can reproduce it with debugging
+> > KK> enabled (I'm also trying) we can try to fix it.
+> > 
+> > Please try to simulate user who is over soft quota and is out of grace period. 
+> > I'm trying to do so as well, but currently quite busy with other tasks :(
+> 
+> I'm not sure whether the following is the issue you met, but:
+> 
+> dqsync from sys/ufs/ufs/ufs_quota.c calls vn_start_secondary_write()
+> unconditionally. As result, mp->mnt_secondary_accwrites counter
+> from the struct mount will always increase after the entry to the dqsync.
+> ffs_snapshot calls ffs_sync, that calls dsync, that
+> iterates over vnodes and calls dqsync on them.
+> And, after the qsync, ffs_sync checks whether mp->mnt_secondary_accwrites
+> changes by calling softdep_check_suspend (see line 1221 of ffs_vfsops.c).
+> If changed, ffs_sync would restart the syncing loop, that never finishes.
+> 
+> This is very strange, since if true, it basicaly means that snapshots
+> and quotas shall lead to immediate deadlock ...
+> 
+> The following patch moves call to vn_start_secondary_write after
+> check for DQ_MOD. Please, try it.

Your patch must not be against HEAD, because in HEAD we have:

	if ((dq->dq_flags & DQ_MOD) == 0)
		return (0);
	if ((dqvp = dq->dq_ump->um_quotas[dq->dq_type]) == NULLVP)
		panic("dqsync: file");
	(void) vn_start_secondary_write(dqvp, &mp, V_WAIT);
	if (vp != dqvp)
		vn_lock(dqvp, LK_EXCLUSIVE | LK_RETRY, td);

As you can see DQ_MOD is checked before vn_start_secondary_write().

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20060426/d5096401/attachment.pgp