ZFS panic: empty ZFS ACL

[James R. Van Artsdalen]

  amd64
  Version String: FreeBSD 9.0-CURRENT #0 r214378M: Sun Nov 28 07:52:25
CST 2010 root at kraken.housenet.jrv:/usr/obj/usr/src/sys/GENERIC
  Panic String: empty ZFS ACL

I got this panic via "ls -l" after copying in a very old pool via zfs
send/recv: the pool originated on Macintosh ZFS just after Apple first
released the initial build of that.

Steps:

kraken:/root# zpool create STUFF raidz2 ada{0,1,2,3,8,9,10,11} # new
destination
kraken:/root# zpool import fearhome # foreign, old pool
kraken:/root# zfs umount fearhome
kraken:/root# zfs snapshot -r fearhome at now
kraken:/root# zfs create STUFF/fearhome
kraken:/root# zfs send -R fearhome at now | zfs recv -duvF STUFF/fearhome
receiving full stream of fearhome at now into STUFF/fearhome at now
received 1.52TB stream in 85275 seconds (18.7MB/sec)
kraken:/root# zpool export fearhome
kraken:/root# ls -l /STUFF/fearhome/
total 6951425
Read from remote host kraken: Operation timed out
Connection to kraken closed.

relevant dump backtrace:

#9  0xffffffff805cb490 in panic (fmt=Variable "fmt" is not available.
)
    at /usr/src/sys/kern/kern_shutdown.c:574
#10 0xffffffff810c9f85 in acl_from_aces (aclp=Variable "aclp" is not
available.
)
    at
/usr/src/sys/modules/zfs/../../cddl/compat/opensolaris/kern/opensolaris_acl.c:108
#11 0xffffffff8114aa3a in zfs_freebsd_getacl (ap=0xffffff82472be840)
    at
/usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c:5314
#12 0xffffffff80645701 in vacl_get_acl (td=Variable "td" is not available.
) at vnode_if.h:1221
#13 0xffffffff806459bf in __acl_get_link (td=0xffffff00088bf000,
    uap=0xffffff82472bebb0) at /usr/src/sys/kern/vfs_acl.c:355
#14 0xffffffff8060caea in syscallenter (td=0xffffff00088bf000,
    sa=0xffffff82472beba0) at /usr/src/sys/kern/subr_trap.c:318
#15 0xffffffff808c612c in syscall (frame=0xffffff82472bec40)
    at /usr/src/sys/amd64/amd64/trap.c:939
#16 0xffffffff808b0422 in Xfast_syscall ()
    at /usr/src/sys/amd64/amd64/exception.S:381
#17 0x000000080096f4fc in ?? ()
Previous frame inner to this frame (corrupt stack?)