system locks up after a few unsuccessful attempts to create a snapshot of /

hi there,

i was trying to create a snapshot of my root fs. the commands i used were
1) mksnap_ffs /.snap/snap1
   and
2) mount -u -o snapshot /.snap/snap1 /

both command failed with EAGAIN and the following was output to the console:

Sep  6 18:05:56 otaku kernel: fsync: giving up on dirty
Sep  6 18:05:56 otaku kernel: 0xffffff000552dd20: tag devfs, type VCHR
Sep  6 18:05:56 otaku kernel: usecount 1, writecount 0, refcount 1372 mountedhere 0xffffff0005650a00
Sep  6 18:05:56 otaku kernel: flags ()
Sep  6 18:05:56 otaku kernel: v_object 0xffffff000568fbd0 ref 0 pages 5486
Sep  6 18:05:56 otaku kernel: lock type devfs: EXCL by thread 0xffffff006b473840 (pid 48144)
Sep  6 18:05:56 otaku kernel: dev ufs/rootfs
Sep  6 18:08:19 otaku sudo:  arundel : TTY=pts/0 ; PWD=/usr/src/sbin/mksnap_ffs ; USER=root ; COMMAND=/sbin/mksnap_ffs /.snap/snapshot1
Sep  6 18:08:29 otaku sudo:  arundel : TTY=pts/0 ; PWD=/usr/src/sbin/mksnap_ffs ; USER=root ; COMMAND=/sbin/mksnap_ffs /.snap/snapshot1
Sep  6 18:09:13 otaku kernel: fsync: giving up on dirty
Sep  6 18:09:14 otaku kernel: 0xffffff000552dd20: tag devfs, type VCHR
Sep  6 18:09:14 otaku kernel: usecount 1, writecount 0, refcount 1373 mountedhere 0xffffff0005650a00
Sep  6 18:09:14 otaku kernel: flags ()
Sep  6 18:09:14 otaku kernel: v_object 0xffffff000568fbd0 ref 0 pages 5482
Sep  6 18:09:14 otaku kernel: lock type devfs: EXCL by thread 0xffffff0059000840 (pid 48159)
Sep  6 18:09:14 otaku kernel: dev ufs/rootfs
Sep  6 18:09:14 otaku kernel: fsync: giving up on dirty
Sep  6 18:09:14 otaku kernel: 0xffffff000552dd20: tag devfs, type VCHR
Sep  6 18:09:14 otaku kernel: usecount 1, writecount 0, refcount 1373 mountedhere 0xffffff0005650a00
Sep  6 18:09:14 otaku kernel: flags ()
Sep  6 18:09:14 otaku kernel: v_object 0xffffff000568fbd0 ref 0 pages 5482
Sep  6 18:09:14 otaku kernel: lock type devfs: EXCL by thread 0xffffff0059000840 (pid 48159)
Sep  6 18:09:14 otaku kernel: dev ufs/rootfs
Sep  6 18:11:50 otaku sudo:  arundel : TTY=pts/6 ; PWD=/usr/home/arundel ; USER=root ; COMMAND=/sbin/mount -u -o snapshot /.snap/snap1 /
Sep  6 18:12:33 otaku kernel: fsync: giving up on dirty
Sep  6 18:12:34 otaku kernel: 0xffffff000552dd20: tag devfs, type VCHR
Sep  6 18:12:34 otaku kernel: usecount 1, writecount 0, refcount 1383 mountedhere 0xffffff0005650a00
Sep  6 18:12:34 otaku kernel: flags ()
Sep  6 18:12:34 otaku kernel: v_object 0xffffff000568fbd0 ref 0 pages 5514
Sep  6 18:12:34 otaku kernel: lock type devfs: EXCL by thread 0xffffff006bd6f000 (pid 48194)
Sep  6 18:12:34 otaku kernel: dev ufs/rootfs
Sep  6 18:12:34 otaku kernel: fsync: giving up on dirty
Sep  6 18:12:34 otaku kernel: 0xffffff000552dd20: tag devfs, type VCHR
Sep  6 18:12:34 otaku kernel: usecount 1, writecount 0, refcount 1383 mountedhere 0xffffff0005650a00
Sep  6 18:12:34 otaku kernel: flags ()
Sep  6 18:12:34 otaku kernel: v_object 0xffffff000568fbd0 ref 0 pages 5514
Sep  6 18:12:34 otaku kernel: lock type devfs: EXCL by thread 0xffffff006bd6f000 (pid 48194)
Sep  6 18:12:34 otaku kernel: dev ufs/rootfs

after about 4 attempts my system stopped responding. after a reboot both
commands succeed without any issues.

i'm running HEAD (r212123; amd64).

otaku% mount -p
/dev/ufs/rootfs		/			ufs	noatime		1 1
devfs			/dev			devfs	rw		0 0
devfs			/usr/compat/linux/dev	devfs	rw		0 0
linprocfs		/usr/local/gentoo-stage3/proc linprocfs	rw		0 0
linsysfs		/usr/local/gentoo-stage3/sys linsysfs	rw		0 0
devfs			/usr/local/gentoo-stage3/dev devfs	rw		0 0
otaku% tunefs -p /
tunefs: POSIX.1e ACLs: (-a)                                disabled
tunefs: NFSv4 ACLs: (-N)                                   disabled
tunefs: MAC multilabel: (-l)                               disabled
tunefs: soft updates: (-n)                                 enabled
tunefs: soft update journaling: (-j)                       enabled
tunefs: gjournal: (-J)                                     disabled
tunefs: maximum blocks per file in a cylinder group: (-e)  2048
tunefs: average file size: (-f)                            16384
tunefs: average number of files in a directory: (-s)       64
tunefs: minimum percentage of free space: (-m)             8%
tunefs: optimization preference: (-o)                      time
tunefs: volume label: (-L)                                 rootfs
otaku% df -h
Filesystem         Size    Used   Avail Capacity  Mounted on
/dev/ufs/rootfs    218G    186G     14G    93%    /
devfs              1.0K    1.0K      0B   100%    /dev
devfs              1.0K    1.0K      0B   100%    /usr/compat/linux/dev
linprocfs          4.0K    4.0K      0B   100%    /usr/local/gentoo-stage3/proc
linsysfs           4.0K    4.0K      0B   100%    /usr/local/gentoo-stage3/sys
devfs              1.0K    1.0K      0B   100%    /usr/local/gentoo-stage3/dev

cheers.
alex

-- 
a13x