kern/184677: ZFS snapshot umount kernel panic

[Richard Kojedzinszky]

>Number:         184677
>Category:       kern
>Synopsis:       ZFS snapshot umount kernel panic
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Dec 11 06:10:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Richard Kojedzinszky
>Release:        stable/10, releng/9.2
>Organization:
>Environment:
FreeBSD freebsd10 10.0-PRERELEASE FreeBSD 10.0-PRERELEASE #9 57a89d6(stable/10)-dirty: Mon Dec  9 11:11:30 CET 2013     root at freebsd10:/usr/obj/usr/src/sys/BSD  amd64
>Description:
Accessing ZFS snapshots and unmounting them parallell causes the system to panic. 

In a real server setup, where unix users exists, they are able to access .zfs/snapshot/ directories, which causes snapshots to be mounted. The system may be set up to clean those mounts, umount them at some time. Then a panic may occur.
>How-To-Repeat:
Run the script at http://pastebin.com/Bf15sMhd on an empty ZFS dataset with a snapshot.
>Fix:


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