panic: kernel diagnostic assertion "xbdi->xbdi_pendingreqs == 0" failed

[Jeff Rizzo <riz%tastylime.net@localhost>]

I've triggered this KASSERT on my dom0 twice in the last hour;  once 
with a very -current kernel, once with a kernel a few weeks old.  
Happens with a lot of i/o activity in the domUs.

Anything I should get to help track down what's going on?

+j

panic: kernel diagnostic assertion "xbdi->xbdi_pendingreqs == 0" failed: 
file 
"/Users/riz/Documents/code/netbsd/src/sys/arch/xen/xen/xbdback_xenbus.c", line 
1024
cpu0: Begin traceback...
kern_assert() at netbsd:kern_assert+0x2d
xbdback_co_cache_flush() at netbsd:xbdback_co_cache_flush+0xae
xbdback_trampoline() at netbsd:xbdback_trampoline+0x5b
xbdback_evthandler() at netbsd:xbdback_evthandler+0x28
evtchn_do_event() at netbsd:evtchn_do_event+0x160
call_evtchn_do_event() at netbsd:call_evtchn_do_event+0xd
hypervisor_callback() at netbsd:hypervisor_callback+0xa2
idle_loop() at netbsd:idle_loop+0x16f
cpu0: End traceback...
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip ffffffff80223995 cs e030 rflags 246 cr2  
7f7fed636000 cpl 8 rsp ffffa000122a4888
Stopped in pid 0.2 (system) at  netbsd:breakpoint+0x5:  leave
breakpoint() at netbsd:breakpoint+0x5
panic() at netbsd:panic+0x27f
kern_assert() at netbsd:kern_assert+0x2d
xbdback_co_cache_flush() at netbsd:xbdback_co_cache_flush+0xae
xbdback_trampoline() at netbsd:xbdback_trampoline+0x5b
xbdback_evthandler() at netbsd:xbdback_evthandler+0x28
evtchn_do_event() at netbsd:evtchn_do_event+0x160
call_evtchn_do_event() at netbsd:call_evtchn_do_event+0xd
hypervisor_callback() at netbsd:hypervisor_callback+0xa2
idle_loop() at netbsd:idle_loop+0x16f
ds          104
es          1008
fs          2b26
gs          4888
rdi         6
rsi         0
rbp         ffffa000122a4888
rbx         104
rdx         ffffffff
rcx         8
rax         ffffffff
r8          ffffffff80c28280    cpu_info_primary
r9          1
r10         0
r11         ffffffff80e4e922
r12         ffffffff80b0e6e0    
__link_set_malloc_types_sym_M_PROP_ARRAY+0x60a28

r13         deadbeef
r14         ffffa00000e5dc80
r15         ffffa000122a4b18
rip         ffffffff80223995    breakpoint+0x5
cs          e030
rflags      246
rsp         ffffa000122a4888
ss          e02b
netbsd:breakpoint+0x5:  leave
db>