kern/85466: [PANIC] mount_nullfs triggers locking against self

[Xin LI]

>Number:         85466
>Category:       kern
>Synopsis:       [PANIC] mount_nullfs triggers locking against self
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Aug 30 09:10:20 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Xin LI
>Release:        FreeBSD 6.0-BETA3 i386
>Organization:
The GeekCN Community
>Environment:
System: FreeBSD tarsier.delphij.net 6.0-BETA3 FreeBSD 6.0-BETA3 #4: Mon Aug 29 03:51:10 CST 2005 delphij at tarsier.delphij.net:/usr/obj/usr/src/sys/TARSIER i386

	FreeBSD 7.0-CURRENT affected as well.

>Description:
	An easily reproducable panic can be triggered with mount_nullfs
and mount_nfs.

>How-To-Repeat:
	- Create two directories, say, /usr/ports and /mnt
	- do mount_nullfs /usr/ports /mnt
	- do mount_nfs something onto /usr/ports
	- do mount_nullfs /usr/ports /mnt
	- cd /mnt && ls, the system will panic immediately

>Fix:

	I don't have a patchset to correct this (yet).
>Release-Note:
>Audit-Trail:
>Unformatted: