kern/96644: crash after mount/umount disturbance: fatal trap 12

[Arne Woerner]

>Number:         96644
>Category:       kern
>Synopsis:       crash after mount/umount disturbance: fatal trap 12
>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:   Tue May 02 06:40:13 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     Arne Woerner
>Release:        R6.0
>Organization:
>Environment:
FreeBSD neo.riddick.homeunix.org 6.0-RELEASE FreeBSD 6.0-RELEASE #10:
Mon Apr 10 15:10:38 UTC 2006
aw at neo.riddick.homeunix.org:/usr/src/sys/i386/compile/NEO  i386

>Description:
Once upon a time I looked through my self made DVDs. When I mounted a DVD
twice at the same mount point and read from that DVD and unmounted the DVD
once and read again from it, the system crashed.

This is not really bad, since I usually know, what is mounted...
But it might be nicer, if the kernel could cope with such things...
>How-To-Repeat:
cd /opt/tmp
dd if=/dev/zero of=a bs=1m count=200
mdconfig -a -t vnode -f a
newfs /dev/md0
mount /dev/md0 /mnt
dd if=/dev/zero of=/mnt/a bs=1m count=100
umount /mnt
mount -r /dev/md0 /mnt
mount -r /dev/md0 /mnt
dd if=/mnt/a of=/dev/null bs=1m
umount /mnt
dd if=/mnt/a of=/dev/null bs=1m
*cloink*

kernel says:
fatal trap 12: page fault while in kernel mode
fault virtual address = 0x0
fault code = supervisor read, page not present
>Fix:

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