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Date:      Wed, 13 Feb 2013 08:37:01 -0800
From:      Tim Gustafson <tjg@ucsc.edu>
To:        freebsd-fs@freebsd.org
Subject:   FreeBSD 9.1 ZFS-Related Crash
Message-ID:  <CAPyBAS63akKq5DoU1W_TTKfDcNHzrO4Z_uiOwEXKdVEBhpZSRA@mail.gmail.com>

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Hi,

I'm not sure how to report this as an official bug, or if it even
qualifies as one.

We're running ZFS on a FreeBSD 9.1 machine.  Our zpool is version 28
and our zfs file systems are version 5.

Some of our users still have individual ZFS file systems for their
home directories.  One in particular also has a bunch of cron jobs
that run every few minutes on different systems that access his home
directory via NFSv3.  In order to take his home directory off-line, I
removed him from /etc/exports and re-started mountd.  When I attempted
to change the mount point of his ZFS file system, the server crashed.
When the server came back up and I attempted to change the mount point
a second time, the server crashed again.

I've done this hundreds of times for other users, and have had maybe 5
or 6 other crashes on other people's home directories as well.  So,
it's a somewhat reproducible bug, but it's not very consistent.

My best guess is that if you attempt to un-mount a ZFS file system
when there is still some sort of NFS activity, it causes the system to
crash.  But, most of the time it seems that if you attempt to unmount
a file system that is still in use, the unmount command returns an
error stating that the file system is still in use.  So there's some
certain type of NFS activity that seems to cause the issue - whether
it's perhaps trying to open a file right as the file system is being
unmounted, or maybe having a file locked but not open...I just don't
know which condition is the culprit.

I have some spare hardware that I could use to attempt to reproduce
this crash, but I wanted to ping the group first to see if anyone else
has seen this issue.  Is this a known issue?  Has anyone else seen
this sort of behavior?

-- 

Tim Gustafson
tjg@ucsc.edu
831-459-5354
Baskin Engineering, Room 313A



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