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

[Ben Schumacher]

>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
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Dec 17 16:50:02 UTC 2009
>Closed-Date:
>Last-Modified:
>Originator:     Ben Schumacher
>Release:        FreeBSD 8.0-RELEASE-p1 i386
>Organization:
>Environment:
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
>Description:
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.
>How-To-Repeat:
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.
>Fix:
Workaround: Don't 'zfs rename' a mounted snapshot. It'd be nice, however, if
the OS blocked the operations and didn't panic.


>Release-Note:
>Audit-Trail:
>Unformatted: