(kgdb) bt
#0  sched_switch (td=0xfffffe0002fd9460, newtd=0xfffffe00025f8000, flags=Variable "flags" is not available.
)
    at /usr/src/sys/kern/sched_ule.c:1853
#1  0xffffffff806eebcd in mi_switch (flags=260, newtd=0x0)
    at /usr/src/sys/kern/kern_synch.c:450
#2  0xffffffff80725d33 in sleepq_switch (wchan=0xffffff8000da29e0, pri=96)
    at /usr/src/sys/kern/subr_sleepqueue.c:538
#3  0xffffffff8072696d in sleepq_wait (wchan=0xffffff8000da29e0, pri=96)
    at /usr/src/sys/kern/subr_sleepqueue.c:617
#4  0xffffffff806ef369 in _sleep (ident=0xffffff8000da29e0,
    lock=0xffffff8000d918e0, priority=Variable "priority" is not available.
) at /usr/src/sys/kern/kern_synch.c:234
#5  0xffffff8000b709af in afs_osi_Sleep (event=0xffffff8000da29e0)
    at /usr/ports/net/openafs/work/openafs-1.6.0pre2/src/afs/FBSD/osi_sleep.c:142
#6  0xffffff8000b63c48 in osi_StopListener ()
    at /usr/ports/net/openafs/work/openafs-1.6.0pre2/src/rx/FBSD/rx_knet.c:116
#7  0xffffff8000b73f98 in afs_shutdown ()
    at /usr/ports/net/openafs/work/openafs-1.6.0pre2/src/afs/afs_call.c:1284
#8  0xffffff8000b7ef4f in afs_unmount (mp=0xfffffe0002d95000, flags=Variable "flags" is not available.
)
    at /usr/ports/net/openafs/work/openafs-1.6.0pre2/src/afs/FBSD/osi_vfsops.c:237
#9  0xffffffff80776d1c in dounmount (mp=0xfffffe0002d95000, flags=134217728,
    td=Variable "td" is not available.
) at /usr/src/sys/kern/vfs_mount.c:1302
#10 0xffffffff807772be in unmount (td=0xfffffe0002fd9460,
    uap=0xffffff8090a51bc0) at /usr/src/sys/kern/vfs_mount.c:1188
#11 0xffffffff80728bca in syscallenter (td=0xfffffe0002fd9460,
    sa=0xffffff8090a51bb0) at /usr/src/sys/kern/subr_trap.c:329
#12 0xffffffff809e1c9c in syscall (frame=0xffffff8090a51c50)
    at /usr/src/sys/amd64/amd64/trap.c:908