ZFS hang in production on 8.2-RELEASE

[Luke Marsden]

Hi all,

I've just noticed a "partial" ZFS deadlock in production on 8.2-RELEASE.

FreeBSD XXX 8.2-RELEASE FreeBSD 8.2-RELEASE #0 r219081M: Wed Mar  2
08:29:52 CET 2011     root at www4:/usr/obj/usr/src/sys/GENERIC  amd64

There are 9 'zfs rename' processes and 1 'zfs umount -f' processes hung.
Here is the procstat for the 'zfs umount -f':

13451 104337 zfs              -                mi_switch+0x176
sleepq_wait+0x42 _sleep+0x317 zfsvfs_teardown+0x269 zfs_umount+0x1c4
dounmount+0x32a unmount+0x38b syscallenter+0x1e5 syscall+0x4b
Xfast_syscall+0xe2 

And the 'zfs rename's all look the same:

20361 101049 zfs              -                mi_switch+0x176
sleepq_wait+0x42 __lockmgr_args+0x743 vop_stdlock+0x39 VOP_LOCK1_APV
+0x46 _vn_lock+0x47 lookup+0x6e1 namei+0x53a kern_rmdirat+0xa4
syscallenter+0x1e5 syscall+0x4b Xfast_syscall+0xe2 

An 'ls' on a directory which contains most of the system's ZFS
mount-points (/hcfs) also hangs:

30073 101466 gnuls            -                mi_switch+0x176
sleepq_wait+0x42 __lockmgr_args+0x743 vop_stdlock+0x39 VOP_LOCK1_APV
+0x46 _vn_lock+0x47 zfs_root+0x85 lookup+0x9b8 namei+0x53a vn_open_cred
+0x3ac kern_openat+0x181 syscallenter+0x1e5 syscall+0x4b Xfast_syscall
+0xe2 

If I truss the 'ls' it hangs on the stat syscall:
stat("/hcfs",{ mode=drwxr-xr-x ,inode=3,size=2012,blksize=16384 }) = 0
(0x0)

There is also a 'find -s / ! ( -fstype zfs ) -prune -or -path /tmp
-prune -or -path /usr/tmp -prune -or -path /var/tmp -prune -or
-path /var/db/portsnap -prune -or -print' running which is also hung:

 2650 101674 find             -                mi_switch+0x176
sleepq_wait+0x42 __lockmgr_args+0x743 vop_stdlock+0x39 VOP_LOCK1_APV
+0x46 _vn_lock+0x47 zfs_root+0x85 lookup+0x9b8 namei+0x53a vn_open_cred
+0x3ac kern_openat+0x181 syscallenter+0x1e5 syscall+0x4b Xfast_syscall
+0xe2 

However I/O to the presently mounted filesystems continues to work (even
on parts of filesystems which are unlikely to be cached), and 'zfs list'
showing all the filesystems (3,500 filesystems with ~100 snapshots per
filesystem) also works.

Any activity on the structure of the ZFS hierarchy *under the hcfs
filesystem* crashes, such as a 'zfs create hpool/hcfs/test':

70868 101874 zfs              -                mi_switch+0x176
sleepq_wait+0x42 __lockmgr_args+0x743 vop_stdlock+0x39 VOP_LOCK1_APV
+0x46 _vn_lock+0x47 lookup+0x6e1 namei+0x53a kern_mkdirat+0xce
syscallenter+0x1e5 syscall+0x4b Xfast_syscall+0xe2 

BUT "zfs create hpool/system/opt/hello" (a ZFS filesystem in the same
pool, but not rooted on hpool/hcfs) does not hang, and succeeds
normally.

procstat -kk on the zfskern process gives:

  PID    TID COMM             TDNAME
KSTACK                       
    5 100045 zfskern          arc_reclaim_thre mi_switch+0x176
sleepq_timedwait+0x42 _cv_timedwait+0x134 arc_reclaim_thread+0x2a9
fork_exit+0x118 fork_trampoline+0xe 
    5 100046 zfskern          l2arc_feed_threa mi_switch+0x176
sleepq_timedwait+0x42 _cv_timedwait+0x134 l2arc_feed_thread+0x1ce
fork_exit+0x118 fork_trampoline+0xe 
    5 100098 zfskern          txg_thread_enter mi_switch+0x176
sleepq_wait+0x42 _cv_wait+0x129 txg_thread_wait+0x79 txg_quiesce_thread
+0xb5 fork_exit+0x118 fork_trampoline+0xe 
    5 100099 zfskern          txg_thread_enter mi_switch+0x176
sleepq_timedwait+0x42 _cv_timedwait+0x134 txg_thread_wait+0x3c
txg_sync_thread+0x365 fork_exit+0x118 fork_trampoline+0xe 

Any ideas on what might be causing this?

Thank you for supporting ZFS on FreeBSD!

-- 
Best Regards,
Luke Marsden
CTO, Hybrid Logic Ltd.

Web: http://www.hybrid-cluster.com/
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