misc/164472: fsck -B panics on particular data inconsistency

[Eugene M. Zheganin]

>Number:         164472
>Category:       misc
>Synopsis:       fsck -B panics on particular data inconsistency
>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 Jan 25 09:00:29 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Eugene M. Zheganin
>Release:        8.2-RELEASE
>Organization:
RealService LLC
>Environment:
FreeBSD elf.hq.norma.perm.ru 8.2-RELEASE FreeBSD 8.2-RELEASE #1: Thu May  5 19:14:23 YEKST 2011     emz at ns.hq.norma.perm.ru:/usr/obj/usr/src/sys/ELF  i386
>Description:
fsck -B panics on particular inconsistencies.
I got one machine that sometimes locks up (probably die to some other bug), and after reset when it runs fsck -B it leads to panic.

Since this happens quite often last time I created an image on a partition that makes FreeBSD panic.

Unfortunately this machine doesn't run a debug kernel, and, due to a bug when FreeBSD reboots immidiately upon a key press from a screen where it says 'Automatic reboot in 15 seconds, press any key to abort' (which is still unreported for some reason, while lots of people confirm its existance) I was (and I am) unable to capture a panic screen.

But, since I have an image, everyone can easily reproduce this panic.
This is 100% reproduceable, at least I've done it 5 times on a test machine and got a panic each time. Unfortunately, this machine is too old to build debug kernel in some reasonable amount of time (I really think anyone will download this image faster than I will build a debug kernel).

So... here comes the image in case someone is interested.

Attention, FreeBSD panics only when fsck is run with -B. Ordinary fsck run doesn't panic and is able to successfully resolve all the filesystem errors.
>How-To-Repeat:
Get an image from http://tech.norma.perm.ru/files/var.dsk (sorry, this link is about a couple of megabits, my really broadband link is served by a server from my previous report with a buggy pf route-to/reply-to, so I'm using this old server). Mount it read-write (I didn't test it on an unmounted or read-only image). Like this:

mdconfig -a -t vnode -f var.dsk
mount /dev/md0 /mnt/panic

Run an fsck (since it's a partition image you need to manually specify the fsck of the type needed):

fsck_4.2bsd -B /dev/md0
<here it panics>
>Fix:
Run fsck without -B.

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