kern/105056: FS can not be remounted read-only, if a running process' executable was modified

[Mikhail T.]

>Number:         105056
>Category:       kern
>Synopsis:       FS can not be remounted read-only, if a running process' executable was modified
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Nov 02 01:20:23 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     Mikhail T.
>Release:        FreeBSD 6.2-PRERELEASE amd64
>Organization:
Virtual Estates, Inc.
>Environment:
System: FreeBSD aldan.algebra.com 6.2-PRERELEASE FreeBSD 6.2-PRERELEASE #1: Sat Sep 30 16:33:20 EDT 2006 root at aldan.algebra.com:/meow/obj/var/src/sys/SILVER amd64

>Description:

	If a running process' image is overwritten (such by install-ing
	a new version), the hosting file-system can not be remounted
	read-only until the process exits.

>How-To-Repeat:

	Here is an example. My / is routinely mounted read-only:

		% mount -orw -u /
		% cp -p /bin/sleep /tmp/
		% sleep 3600 &
		% install -m 755 -o root -g bin /tmp/sleep /bin/sleep
		% mount -oro -u /
		mount: /dev/ad4s1a: Device busy

	Ending the running process, allows the read-only remount:

		% kill %
		% mount -oro -u /
		%

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