recent changes in Giant usage -> panic

I cvsup'ed a few hours ago and did the buildworld and buildkernel drill.
I installed the new kernel, rebooted, and got this panic while mtree was
running in installworld.

--------------------------------------------------------------
>>> Making hierarchy
--------------------------------------------------------------
cd /usr/src; /usr/obj/usr/src/make.i386/make -f Makefile.inc1 hierarchy
cd /usr/src/etc;                /usr/obj/usr/src/make.i386/make distrib-dirs
mtree -deU  -f /usr/src/etc/mtree/BSD.root.dist -p /


panic: mutex Giant not owned at /usr/src/sys/kern/vfs_subr.c:899
at line 719 in file /usr/src/sys/kern/kern_mutex.c
cpuid = 0; 
Debugger("panic")
Stopped at      Debugger+0x46:  xchgl   %ebx,in_Debugger.0
db> tr
Debugger(c07d2da1) at Debugger+0x46
__panic(c07d217c,2cf,c07d22e8,c07d2423,c07daecf) at __panic+0x13d
_mtx_assert(c0893860,1,c07daecf,383,c68931b0) at _mtx_assert+0xc2
vinvalbuf(c6893104,1,0,c6872690,0,0) at vinvalbuf+0x25
vclean(c6893104,8,c6872690,c6893104,c6893104) at vclean+0x97
vgonel(c6893104,c6872690,c6893104,0,c07daecf) at vgonel+0x4d
vgone(c6893104) at vgone+0x28
pfs_exit(0,c6871898,c648c68c,0,c07d0695) at pfs_exit+0x3f
exit1(c6872690,0,e7b11d40,c076bca7,c6872690) at exit1+0x2bd
exit1(c6872690,e7b11d14,1,11,296) at exit1
syscall(2f,2f,2f,4814a740,bfbfea48) at syscall+0x217
Xint0x80_syscall() at Xint0x80_syscall+0x1d
--- syscall (1, FreeBSD ELF32, sys_exit), eip = 0x480c5163, esp = 0xbfbfe9ac, ebp = 0xbfbfe9c8 ---



I've cvsup'ed again, but I didn't see any commits that look promising.
The only new commit to sys/kern was the change to HZ for amd64.