panic when umounting a msdosfs mount: "VOP_STDCLOSE: BAD WRITECOUNT 0xf2629e68 0"

[Rumko <rumcic@xxxxxxxxx>]

After playing with my mobile phone (mounted it's memory card with mount -t
msdosfs), a umount triggered the panic (well, I did run sync a second or 2
before doing a umount). The memory dump is at leaf:~rumko/crash/19.05.2008/
and the backtrace (including the kernel message buffer that kgdb prints) is
here:

Unread portion of the kernel message buffer:
panic: VOP_STDCLOSE: BAD WRITECOUNT 0xf2629e68 0
 
mp_lock = 00000001; cpuid = 1
boot() called on cpu#1
 
syncing disks... 3 ad8: WARNING - SETFEATURES SET TRANSFER MODE taskqueue
timeout - completing request directly
ad8: TIMEOUT - WRITE_DMA retrying (1 retry left) LBA=12361855
 
done
Uptime: 21h9m5s
 
dumping to dev #ad/0x20041, blockno 4204800
dump 2046 2045 ... 1 0
 
GNU gdb 6.7.1
Copyright (C) 2007 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i386-dragonfly".
(kgdb) bt
#0  dumpsys () at ./machine/thread.h:83
#1  0xc02733c5 in boot (howto=256) at /usr/src/sys/kern/kern_shutdown.c:375
#2  0xc0273688 in panic (fmt=0xc0521f34 "VOP_STDCLOSE: BAD WRITECOUNT %p %d\n")
at /usr/src/sys/kern/kern_shutdown.c:800
#3  0xc02b55f5 in vop_stdclose (ap=0xf49f0bf8)
at /usr/src/sys/kern/vfs_default.c:1191
#4  0xc02caf0f in spec_close (ap=0xf49f0bf8)
at /usr/src/sys/vfs/specfs/spec_vnops.c:763
#5  0xc03c3e6e in ufsspec_close (ap=0xf49f0bf8)
at /usr/src/sys/vfs/ufs/ufs_vnops.c:1947
#6  0xc03c1f44 in ufs_vnoperatespec (ap=0xf49f0bf8)
at /usr/src/sys/vfs/ufs/ufs_vnops.c:2462
#7  0xc02c5f8e in vop_close (ops=0xd3a0c150, vp=0xf2629e68, fflag=3)
at /usr/src/sys/kern/vfs_vopops.c:257
#8  0xc02cf827 in msdosfs_unmount (mp=0xda422060, mntflags=0)
at /usr/src/sys/vfs/msdosfs/msdosfs_vfsops.c:672
#9  0xc02c2f7a in dounmount (mp=0xda422060, flags=0)
at /usr/src/sys/kern/vfs_syscalls.c:705
#10 0xc02c31c7 in sys_unmount (uap=0xf49f0cf0)
at /usr/src/sys/kern/vfs_syscalls.c:590
#11 0xc049a37d in syscall2 (frame=0xf49f0d40)
at /usr/src/sys/platform/pc32/i386/trap.c:1349
#12 0xc0487be6 in Xint0x80_syscall ()
at /usr/src/sys/platform/pc32/i386/exception.s:876
#13 0x0804ace8 in ?? ()
-- 
Regards,
Rumko