port-i386/39898: wapbl kernel diagnostic assertion "head == off"

[Bernd Ernesti <pr200822%veego.de@localhost>]

>Number:         39898
>Category:       port-i386
>Synopsis:       kernel diagnostic assertion "head == off"
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-i386-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Nov 11 19:45:00 +0000 2008
>Originator:     Bernd Ernesti
>Release:        NetBSD 5.99.01
>Organization:
        
>Environment:
System: NetBSD 5.99.01
Architecture: i386
Machine: i386
>Description:

panic: kernel diagnostic assertion "head == off" failed: file 
"/src/sys/kern/vfs_wapbl.c", line 1398
fatal breakpoint trap in supervisor mode
trap type 1 code 0 eip c053d9ac cs 8 eflags 246 cr2 bb923010 ilevel 0
stopped in pid 0.55 (system) at netbsd: breakpoint+0x4: popl %ebp
 
wapbl_flush
ffs_sync
VFS_SYNC
sync_fsync
VOP_FSYNC 
sched_sync

No crash dump because sync didn't return.

>How-To-Repeat:
        Do some file activities.
>Fix: