kern/172348: [unionfs] umount -f of filesystem in use with readonly backed filesystem results in panic

[Garrett Cooper]

>Number:         172348
>Category:       kern
>Synopsis:       [unionfs] umount -f of filesystem in use with readonly backed filesystem results in 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:   Fri Oct 05 03:10:05 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Garrett Cooper
>Release:        9.0-RELEASE
>Organization:
EMC Isilon
>Environment:
Standard amd64 CD image
>Description:
The following resulted in a vary quick kernel panic when booted from the livecd (again, I goofed up the arguments order):

- mount_unionfs /var /tmp/var
- dhclient em0
- umount /var
- umount -f /var
- killall dhclient
- mount_unionfs /tmp/var /var # EBADF
- mount_unionfs /tmp/var /var # EBADF
- Try to inspect /var and BAM kernel panic.

I assume that it was trying to consolidate the outstanding changes to em0.leases, etc and because the unionfs mountpoint went away, things got unhappy really quickly on the UFS side.
>How-To-Repeat:

>Fix:


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