kern/41151: module_thread panics when unloading nfsrv module (uvm_fault)

[kardel%pip.acrys.com@localhost]

>Number:         41151
>Category:       kern
>Synopsis:       module_thread panics when unloading nfsrv module (uvm_fault)
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Apr 05 19:15:00 +0000 2009
>Originator:     Frank Kardel
>Release:        NetBSD 5.99.10
>Organization:
        
>Environment:
System: NetBSD pip.kardel.name 5.99.10 NetBSD 5.99.10 (PIP) #2: Sun Apr 5 
09:09:55 MEST 2009 
kardel%pip.kardel.name@localhost:/fs/raid1a/src/NetBSD/tc-merge/src/obj.i386/sys/arch/i386/compile/PIP
 i386
Architecture: i386
Machine: i386
>Description:
        With today's -current I see a kernel access violation when the module 
thread attempts to auto-unload the nfs_server module.
        The stack trace is roughly as follows:
        turnstile_block
        mutex_vector_enter
        nfsrv_cleancache
        nfsrv_init
        nfsrv_fini
        nfsrv_mod_cmd(?)
        module_do_unload
        module_thread 

        (hand copied)

>How-To-Repeat:
        boot -current-090405 with nfsserver enabled - possibly timing sensible.
>Fix: