kern/141718: kernel panic when 'zfs rename' is used on mounted snapshot

Ben Schumacher me at
Thu Dec 17 16:50:03 UTC 2009

>Number:         141718
>Category:       kern
>Synopsis:       kernel panic when 'zfs rename' is used on mounted snapshot
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Dec 17 16:50:02 UTC 2009
>Originator:     Ben Schumacher
>Release:        FreeBSD 8.0-RELEASE-p1 i386
System: FreeBSD filer.sats.internal 8.0-RELEASE-p1 FreeBSD 8.0-RELEASE-p1 #0: Tue Dec 15 01:05:20 MST 2009 ben at filer.sats.internal:/usr/obj/data/FreeBSD/RELENG_8_0/src/sys/FILER i386
While using RSE's 'snapshot' tool with a ZFS-based system I observed that
calling 'snapshot make' on a drive that has a mounted snapshot causes a panic.
It would appear that the 'zfs rename' call inside the utility being executed
to rename a snapshot that is mounted causes the panic.

Unfortunately I don't have a dump because the system appeared to hang during
the panic (no automatic reboot), so I had to manually power cycle it to get
it back up.
1. Create zfs snapshot of drive.
2. Mount zfs snapshot somewhere on system.
3. Use 'zfs rename' to chnage the name of the mounted snapshot.
4. Observe kernel panic.
Workaround: Don't 'zfs rename' a mounted snapshot. It'd be nice, however, if
the OS blocked the operations and didn't panic.


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