kern/177536: [zfs] zfs livelock (deadlock) with high write-to-disk load

[Martin Birgmeier]

The following reply was made to PR kern/177536; it has been noted by GNATS.

From: Martin Birgmeier <Martin.Birgmeier at aon.at>
To: bug-followup at FreeBSD.org, Andriy Gapon <avg at FreeBSD.org>
Cc:  
Subject: Re: kern/177536: [zfs] zfs livelock (deadlock) with high write-to-disk
 load
Date: Sat, 27 Apr 2013 11:40:16 +0200

 So it happened again... same system (9.1.0 release), except that the
 kernel has been recompiled with options DDB, KDB, and STACK.
 
 I ran procstat -kk -a (twice). Output can be found in
 http://members.aon.at/xyzzy/procstat.-kk.-a.1.gz and
 http://members.aon.at/xyzzy/procstat.-kk.-a.2.gz, respectively. I also
 started kgdb in script(1), executing "thread apply all bt" in it. Output
 can be found in http://members.aon.at/xyzzy/kgdb.thread.apply.all.bt.gz.
 
 More info on the "test case":
 - As described in the initial report, / is a UFS GPT partition on one of
 6 SATA disks. There exists a zpool "hal.1" on one (other) GPT partition
 on each of these disks.
 - VirtualBox is run by a user whose home dir is on one of the zfs file
 systems.
 - First, a big write load to another zfs file system of the same zpool
 was started (160 GB copy from a remote machine).
 - Then, 3 VBoxHeadless instances were started.
 ==> livelock on zfs
 - procstat run twice, then script + kgdb
 - copied output to another machine
 - shutdown the hung machine (via "shutdown -p")
 ==> "some processes would not die"
 ==> "syncing disks" executes until all zeros, then the system just sits
 there with continuous disk activity (obviously from zfs), shutdown does
 not proceed further
 - hard reset
 - on reboot: UFS file system check (no errors), ZFS starts fine and
 seems mostly unaffected (except of course that the 160 GB copy is truncated)
 
 An analysis would be appreciated, and also a hint whether I should
 switch to stable/9 instead.
 
 Regards,
 
 Martin