zfs/unionfs panic on last night's -current

Hi,

I'm experimenting with unionfs for my next FreeBSD book, and found a
reproducible panic. I haven't needed to report a panic for... uh... I
don't think I've done it this century, so I might be a wee bit wrong
in what you need... please correct me if you need other info.

I have a ZFS pool called jails, with two datasets: jails/basejail and
jails/jail1. I want jail1 mounted over basejail, at the jail1 mount
point.

# cd jails
# mount_unionfs -o below basejail/ jail1/

And I get:

panic: solaris assert: cnp->cn_namelen < sizeof(nm), file: /usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c, line: 6213

Info: 

Dump header from device: /dev/gpt/swap0
Architecture: amd64
Architecture Version: 2
Dump Length: 2351693824
Blocksize: 512
Dumptime: Wed Sep  2 10:23:58 2015
Hostname: storm
Magic: FreeBSD Kernel Dump
Version String: FreeBSD 11.0-CURRENT #0 r287374: Tue Sep  1 15:31:17 EDT 2015
root_at_storm:/usr/obj/usr/src/sys/GENERIC
Panic String: solaris assert: cnp->cn_namelen < sizeof(nm), file: /usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c, line: 6213
Dump Parity: 1813619135
Bounds: 3
Dump Status: good

Full panic info at: http://www-old.michaelwlucas.com/core.txt.3
but here's the top of the message.

Unread portion of the kernel message buffer:
panic: solaris assert: cnp->cn_namelen < sizeof(nm), file: /usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c, line: 6213
cpuid = 3
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe085d0cc360
vpanic() at vpanic+0x189/frame 0xfffffe085d0cc3e0
panic() at panic+0x43/frame 0xfffffe085d0cc440
assfail() at assfail+0x1a/frame 0xfffffe085d0cc450
zfs_freebsd_lookup() at zfs_freebsd_lookup+0x47/frame 0xfffffe085d0cc590
VOP_CACHEDLOOKUP_APV() at VOP_CACHEDLOOKUP_APV+0xf1/frame 0xfffffe085d0cc5c0
vfs_cache_lookup() at vfs_cache_lookup+0xd6/frame 0xfffffe085d0cc620
VOP_LOOKUP_APV() at VOP_LOOKUP_APV+0xf1/frame 0xfffffe085d0cc650
relookup() at relookup+0xa1/frame 0xfffffe085d0cc6b0
unionfs_relookup() at unionfs_relookup+0x105/frame 0xfffffe085d0cc710
unionfs_relookup_for_delete() at unionfs_relookup_for_delete+0x56/frame 0xfffffe085d0cc7a0
unionfs_rmdir() at unionfs_rmdir+0xd1/frame 0xfffffe085d0cc800
VOP_RMDIR_APV() at VOP_RMDIR_APV+0xf7/frame 0xfffffe085d0cc830
kern_rmdirat() at kern_rmdirat+0x1bc/frame 0xfffffe085d0cc9a0
amd64_syscall() at amd64_syscall+0x282/frame 0xfffffe085d0ccab0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xfffffe085d0ccab0
--- syscall (137, FreeBSD ELF64, sys_rmdir), rip = 0x80089341a, rsp = 0x7fffffffe8f8, rbp = 0x7fffffffe930 ---
KDB: enter: panic

Thanks!
==ml

-- 
Michael W. Lucas  -  mwlucas_at_michaelwlucas.com, Twitter _at_mwlauthor 
http://www.MichaelWLucas.com/, http://blather.MichaelWLucas.com/