misc/71918: 4.5 disklabel gets damaged when mounted by 5.2.1-R

[Charles Bacon]

>Number:         71918
>Category:       misc
>Synopsis:       4.5 disklabel gets damaged when mounted by 5.2.1-R
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Sep 19 23:10:22 GMT 2004
>Closed-Date:
>Last-Modified:
>Originator:     Chuck Bacon
>Release:        FreeBSD 5.2.1-RELEASE i386
>Organization:
none
>Environment:
FreeBSD daisy.local 5.2.1-RELEASE FreeBSD 5.2.1-RELEASE #0: Mon Feb 23 20:45:55 GMT 2004     root at wv1u.btc.adaptec.com:/usr/obj/usr/src/sys/GENERIC  i386

	(see uname -a above)
>Description:
	Making a new 5.2.1-R slice on an existing 4.5-R system.  Installation
	and boot OK, mount existing 4.5-R filesystems under 5.2.1-R also OK.
	Trouble when booting from 4.5-R on same disk, complaint of bad boot
	block.  Hunting for superblocks succeeds in restoring 4.5-R FS.
	Note UFS1-UFS2 distinction irrelevant here.
>How-To-Repeat:
	1. Create and then boot a 5.2.1-R partition on an otherwise 4.x disk
	2. Mount, then umount, a 4.x partition on the running 5.2.1-R system.
	3. Shutdown -r and now, boot the 4.x OS.
	4. Mount the 4.x partition previously mounted under 5.2.1-R (or try!)
>Fix:
	Sorry, I'm not very smart about fdisk/disklabel/bsdlabel etc.
>Release-Note:
>Audit-Trail:
>Unformatted:
 >Comment:
 	It's been some months, and this box is now all 5.2.1-R, since I have
 	an ATI AGP RADEON board, unknown to the X subsystem on 4.5-R.
 	I may have the details wrong, such as disklabel; I may have used
 	a different approach to restore.