lock order reversal

I've got a lock order reversal.

#uname -a
FreeBSD barleycoren.oikumene.gcd.org 5.1-CURRENT FreeBSD 5.1-CURRENT #1:
Tue Sep 23 21:37:42 JST 2003
hiroo_at_barleycoren.oikumene.gcd.org:/build/usr/src/sys/BARLEYCOREN  i386

Oct 11 18:14:53 barleycoren kernel: 1st 0xc082f060 system map (system map)
_at_ /usr/src/sys/vm/vm_map.c:2236
Oct 11 18:14:53 barleycoren kernel: 2nd 0xc048e560 Giant (Giant)
_at_ /usr/src/sys/vm/vm_map.c:2188

backtrace(c0418e40,c048e560,c0416343,c0416343,c0426bdd) at backtrace+0x17
witness_lock(c048e560,8,c0426bdd,88c,0) at witness_lock+0x5b6
_mtx_lock_flags(c048e560,0,c0426bdd,88c,c026cf6a) at _mtx_lock_flags+0x6a
vm_map_delete(c082f000,dd839000,dd84a000,c456eb6c,c456eb6c) at vm_map_delete+0x1d6
vm_map_remove(c082f000,dd839000,dd84a000,dd547bd4,c029c970) at vm_map_remove+0x55
kmem_free(c082f000,dd839000,11000,c456eb6c,c456eb6c) at kmem_free+0x32
pipe_destroy_write_buffer(c456eb6c,0,c0419360,360,0) at pipe_destroy_write_buffer+0x60
pipe_direct_write(c456eb6c,dd547c80,c0419360,39c,c04b5be8) at pipe_direct_write+0x4e4
pipe_write(c456a000,dd547c80,c444e280,0,c424b5f0) at pipe_write+0x284
dofilewrite(c424b5f0,c456a000,1,80afb40,8000) at dofilewrite+0xe9
write(c424b5f0,dd547d14,c042b83f,3ec,3) at write+0x6e
syscall(2f,2f,2f,80afb40,8000) at syscall+0x233
Xint0x80_syscall() at Xint0x80_syscall+0x1d
--- syscall (4), eip = 0x8050ec3, esp = 0xbfbfee8c, ebp = 0xbfbfeea8 ---