rsync w/ fake-super -> crashes zfs

[javocado]

System specifics:
ZFS version 28
FreeBSD 8.3-RELEASE

We're seeing a repeatable outcome where a remote rsync command like:

rsync -axzHAXS --rsync-path="rsync --fake-super" --exclude '*/rsync.%stat'

backing up to our zfs filesystem (with 15M inodes) will lead to a panic
with output like:

Fatal trap 12: page fault while in kernel modecpuid = 4; apic id =
04fault virtual address   = 0x160fault code              = supervisor
read data, page not presentinstruction pointer     =
0x20:0xffffffff80abb546stack pointer           =
0x28:0xffffff976c62b910frame pointer           =
0x28:0xffffff976c62b9d0code segment            = base 0x0, limit
0xfffff, type 0x1b                        = DPL 0, pres 1, long 1,
def32 0, gran 1processor eflags        = interrupt enabled, resume,
IOPL = 0current process         = 7295 (rsync)[thread pid 7295 tid
101008 ]Stopped at      zfs_freebsd_remove+0x426:       movq
0x160(%rax),%rsi


On the sending side (RHEL, ext3), rsync reports errors like:

rsync: failed to read xattr rsync.%statrsync: failed to write xattr
rsync.%statrsync: get_xattr_names: llistxattr

which we've seen occasionally with other systems when running rsync
with fake-super, but it usually doesn't lead to a crash.*

On the receiving side, other than the crashes, we are seeing a few new
files (that don't exist on the source) named:

rsync.%stat

which correspond to and contain the owner and permission attributes
that should have been stored in the extattr's for the file or
directory. Not sure if they are a red herring, but they're usually not
something we see (perhaps that's related to the --exclude
'*/rsync.%stat' and rsync not being able to cleanup properly).

We are still testing to see if any options in the rsync command
(above) may be contributing to the crash, since fake-super in and of
itself runs fine under basic (rsync -av --rsync-path="rsync
--fake-super" /src /dst) circumstances. But we suspect that the
problem is related to fake-super and its reliance upon extattr's.

What we really need is a solution to the crashing - some way to make
ZFS stop choking on whatever --fake-super produces and/or how it's
interacting with extattr's on ZFS.


Thanks!

* we sometimes also see on the sending side w/ fake-super:
rsync: failed to write xattr rsync.%stat for "xxxxxx/file" : No such file
or directory (2)

when (1) the file exists, (2) it's a symlink
but that isn't happening in this instance. We only mention it here as
another oddity of fake-super + ZFS + extattr