reproducible kernel panic on CURRENT, I/O related

Dear all,

since approximately three weeks I am seeing kernel panics on CURRENT
that are in so far reproducible as that they typically occur when I
run svn up on the ports tree. Hence, it seems I/O related to me. Sorry
that I only now got around to reporting it!

The system is a CURRENT amd64 running ZFS on root w/ GELI. It has the
aesni kernel module loaded. The world and kernel are on SVN r285764.

The kernel stack backtrace looks as follows (transcript):

db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe03d0394830
vpanic() at vpanic+0x189/frame 0xffffe03d03948b0
panic() at panic+0x43/frame 0xfffffe03d0394910
trash_ctor() at trash_ctor+0x48/frame 0xfffffe03d0394920
uma_zalloc_arg() at uma_zalloc_arg+0x573/frame 0xfffffe03d0394990
g_clone_bio() at g_clone_bio+0x1d/frame 0xfffffe03d03949b0
g_part_start() at g_part_start+0x8e/frame 0xfffffe03d0394a30
g_io_schedule_down() at g_io_schedule_down+0xe6/frame 0xfffffe03d0394a60
g_down_procbody() at g_down_procbody+0x7d/frame 0xfffffee03d0394a70
fork_exit() at fork_exit+0x84/frame 0xfffffe03d0394ab0
fork_trampoline at fork_trampoline+0xe/frame 0xfffffe03d0394ab0
--- trap 0, rip = 0, rsp =0xfffffe03d0394b90, rbp = 0---
KDB: enter: panic
[ thread pid 13 tid 100017 ]
Stopped at kdb_enter+0x3e: movq $0,kdb_why

Due to above setup, I cannot provide a core file, sorry.

Please let me know if there is any data you want me to obtain for
debugging. As I said above, it is fairly simple for me to hit the
panic.

Best

Johannes