panic: kernel diagnostic assertion "xbd_io->xio_mapped == 0" failed

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

I have, most unfortunately, changed a number of things at once in the 
last few minutes, so it's hard to say which particular thing is the culprit:

- updated my dom0 to -current as of yesterday (5.99.55), both kernel and 
userland (had been running a slightly older 5.99.55 kernel with a 
5.99.48 userland successfully for a while)

- updated the xentools33 package (or rather rebuilt it)

...and now I get this panic shortly after xendomains starts:

panic: kernel diagnostic assertion "xbd_io->xio_mapped == 0" failed: 
file 
"/Users/riz/Documents/code/netbsd/src/sys/arch/xen/xen/xbdback_xenbus.c", line 
1589
cpu0: Begin traceback...
copyright() at ffffffff809831b5
cpu0: End traceback...
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip ffffffff80216a5d cs e030 rflags 246 cr2  
7f7ff7fd3000 cpl 6 rsp ffffa000122a4958
Stopped in pid 0.2 (system) at  netbsd:breakpoint+0x5:  leave
breakpoint() at netbsd:breakpoint+0x5
panic() at netbsd:panic+0x28c
kern_assert() at netbsd:kern_assert+0x2d
xbdback_co_flush() at netbsd:xbdback_co_flush+0x167
xbdback_trampoline() at netbsd:xbdback_trampoline+0x49
xbdback_evthandler() at netbsd:xbdback_evthandler+0x28
Xresume_xenev6() at netbsd:Xresume_xenev6+0x53
--- interrupt ---
Xspllower() at netbsd:Xspllower+0xe
idle_loop() at netbsd:idle_loop+0xbf
ds          0
es          141c
fs          635
gs          1eb5
rdi         0
rsi         1
rbp         ffffa000122a4958
rbx         ffffa000122a4968
rdx         0
rcx         8
rax         0
r8          ffffffff80bf0a00    cpu_info_primary
r9          0
r10         ffffa000122a4878
r11         ffffffff806f9066    xenconscn_putc
r12         104
r13         ffffffff80ad6de8    
__link_set_malloc_types_sym_M_PROP_ARRAY+0x5f6a0

r14         ffffa000007c6000
r15         0
rip         ffffffff80216a5d    breakpoint+0x5
cs          e030
rflags      246
rsp         ffffa000122a4958
ss          e02b
netbsd:breakpoint+0x5:  leave
db>


Thoughts?
+j