kern/165392: Multiple mkdir/rmdir fails with errno 31

[Jaakko Heinonen]

The following reply was made to PR kern/165392; it has been noted by GNATS.

From: Jaakko Heinonen <jh at FreeBSD.org>
To: Jilles Tjoelker <jilles at stack.nl>
Cc: bug-followup at FreeBSD.org, vvv at colocall.net, mckusick at FreeBSD.org
Subject: Re: kern/165392: Multiple mkdir/rmdir fails with errno 31
Date: Wed, 29 May 2013 19:53:11 +0300

 On 2013-05-27, Jilles Tjoelker wrote:
 > > However, VOP_FSYNC(9) with the MNT_WAIT flag seems not to update the
 > > i_nlink count for a reason unknown to me. I can verify that also by
 > > taking your reproduction recipe above and adding "fsync ." between
 > > "rmdir 1" and "mkdir a".
 > 
 > fsync certainly helps but not as effectively as you'd want. Some
 > combination of sleeps, fsyncs and mkdir attempts appears to be needed.
 
 I have revised the patch and the following version _appears_ to work.
 
 	http://people.freebsd.org/~jh/patches/ufs-check_linkcnt.2.diff
 
 It's still experimental and doesn't handle link(2) or rename(2) at all.
 
 In my testing debug.softdep.linkcnt_retries is increased by one with
 your original reproduction recipe.
 
 > I'm also interested in whether it is safe to call VOP_FSYNC at that
 > point, especially in the case of a rename where a lock on the source
 > directory vnode may be held at the same time.
 
 I think your concern is valid because softdep_fsync() needs to lock
 parent directories. Possibly you can work around the problem by
 unlocking the vnodes, doing fsync and then restarting rename.
 Unfortunately this makes rename even more complex.
 
 -- 
 Jaakko