amd64/133676: umount -f'ing a vnode-based memory disk from off a SMB share caused a reboot

[Rob Bloom]

>Number:         133676
>Category:       amd64
>Synopsis:       umount -f'ing a vnode-based memory disk from off a SMB share caused a reboot
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Apr 13 01:10:05 UTC 2009
>Closed-Date:
>Last-Modified:
>Originator:     Rob Bloom
>Release:        7.1-RELEASE-p1
>Organization:
>Environment:
FreeBSD goosebox.foxular.net 7.1-RELEASE-p1 FreeBSD 7.1-RELEASE-p1 #10: Wed Jan  7 23:33:58 EST 2009     root at goosebox.foxular.net:/usr/obj/usr/src/sys/GOOSEBOX  amd64

>Description:
I had at some point used mdconfig to mount an HD image (with the image on an SMB partition) with an msdos partition  on it to /dev/md0.

I came back a few days later, noticed the disk was still showing as mounted in df, but when I saw the directory was empty, I figured I must have detached the disk without unmounting first. (though while trying to reproduce the bug, this may not have been the case)

I did "umount /mnt/dos" first, getting "umount of /mnt/dos failed: Bad file descriptor", and followed that up with "umount -f /mnt/dos", after which my system immediately rebooted.

Here is the output from /var/log/messages:
Apr 12 20:27:35 goosebox kernel: g_vfs_done():md0s1[READ(offset=512, length=4096)]error = 9
Apr 12 20:27:37 goosebox sudo:   hadley : TTY=ttyp1 ; PWD=/mnt ; USER=root ; COMMAND=/sbin/umount dos
Apr 12 20:27:37 goosebox kernel: g_vfs_done():md0s1[READ(offset=512, length=4096)]error = 9
Apr 12 20:27:38 goosebox sudo:   hadley : TTY=ttyp1 ; PWD=/mnt ; USER=root ; COMMAND=/sbin/umount -f dos
Apr 12 20:28:47 goosebox syslogd: kernel boot file is /boot/kernel/kernel

>How-To-Repeat:
Not quite sure...  I know at the very least it involves creating a memory disk based off a disk image mounted over the network.  It seems that maybe leaving the image mounted for a while and probably rebooting the machine the image is on at some point inbetween caused the disk image to no longer be locatable, causing the reboot when I unmounted it.
>Fix:


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