panic: mutex Giant not owned at vfs_subr.c:1968

While stress testing as root with GENERIC HEAD from Oct 25 15:57
UTC with "option QUOTA" with a filesystem running full I consistently
get this panic:
Tracing pid 42 tid 100046 td 0xc3fc0870
kdb_enter(c091f1d0) at kdb_enter+0x2b
panic(c091e4e9,c0935110,c0929621,7b0,2002,...) at panic+0x14b
_mtx_assert(c0a1f408,1,c0929621,7b0) at _mtx_assert+0x66
vget(c583c930,2002,c3fc0870) at vget+0x4a
vfs_hash_get(c5ee1000,4,2,c3fc0870,e43f4cd4,0,0) at vfs_hash_get+0x8d
ffs_vget(c5ee1000,4,2,e43f4cd4,c0a79618,0,...) at ffs_vget+0x27
clear_remove(c3fc0870,0,c07d7538,c07d7538,0,...) at clear_remove+0xb3
softdep_flush(0,e43f4d38) at softdep_flush+0x73
fork_exit(c07d7538,0,e43f4d38) at fork_exit+0xac
fork_trampoline() at fork_trampoline+0x8

http://people.freebsd.org/~pho/stress/log/cons219.html
-- 
Peter Holm