panic: mutex vm object not owned at src/sys/vm/vm_object.c:695

On a freshly built INVARIANTS kernel.

#0  doadump () at pcpu.h:166
#1  0xc0693984 in boot (howto=260)
    at /d2/emaste/HEAD/src/sys/kern/kern_shutdown.c:409
#2  0xc0693c99 in panic (fmt=0xc090f355 "mutex %s not owned at %s:%d")
    at /d2/emaste/HEAD/src/sys/kern/kern_shutdown.c:565
#3  0xc068b83e in _mtx_assert (m=0xc3b22528, what=0,
    file=0xc092caf4 "/d2/emaste/HEAD/src/sys/vm/vm_object.c", line=695)
    at /d2/emaste/HEAD/src/sys/kern/kern_mutex.c:754
#4  0xc07ecaaf in vm_object_page_clean (object=0xc3b22528, start=0, end=Unhandled dwarf expression opcode 0x93)
    at /d2/emaste/HEAD/src/sys/vm/vm_object.c:695
#5  0xc07734cd in nfs_vinvalbuf (vp=0xc37e0c30, flags=1, td=0xc3b3b1b0,
    intrflg=0) at /d2/emaste/HEAD/src/sys/nfsclient/nfs_bio.c:1316
#6  0xc07719df in nfs_bioread (vp=0xc37e0c30, uio=0xe5dbac64, ioflag=0,
    cred=0xc3be1500) at /d2/emaste/HEAD/src/sys/nfsclient/nfs_bio.c:423
#7  0xc077ccfb in nfs_read (ap=0x0)
    at /d2/emaste/HEAD/src/sys/nfsclient/nfs_vnops.c:981
#8  0xc089c136 in VOP_READ_APV (vop=0x0, a=0xe5dbab9c) at vnode_if.c:631
#9  0xc06f95bf in vn_read (fp=0xc3adf2d0, uio=0xe5dbac64,
    active_cred=0xc3be1500, flags=0, td=0xc3b3b1b0) at vnode_if.h:343
#10 0xc06bad39 in dofileread (td=0xc3b3b1b0, fd=3, fp=0xc3adf2d0,
    auio=0xe5dbac64, offset=Unhandled dwarf expression opcode 0x93) at file.h:241
#11 0xc06babce in kern_readv (td=0xc3b3b1b0, fd=3, auio=0xe5dbac64)
    at /d2/emaste/HEAD/src/sys/kern/sys_generic.c:192
#12 0xc06baaf9 in read (td=0xc3b3b1b0, uap=0x0)
    at /d2/emaste/HEAD/src/sys/kern/sys_generic.c:116
#13 0xc088b236 in syscall (frame=
      {tf_fs = 59, tf_es = 59, tf_ds = 59, tf_edi = 136333456, tf_esi = 0, tf_ebp = -1077945832, tf_isp = -438588060, tf_ebx = 134835488, tf_edx = 0, tf_ecx = 0, tf_eax = 3, tf_trapno = 0, tf_err = 2, tf_eip = 134737971, tf_cs = 51, tf_eflags = 642, tf_esp = -1077945892, tf_ss = 59})
    at /d2/emaste/HEAD/src/sys/i386/i386/trap.c:1016
#14 0xc0875ccf in Xint0x80_syscall ()
    at /d2/emaste/HEAD/src/sys/i386/i386/exception.s:191
#15 0x00000033 in ?? ()