port-xen/52672: 'continue' in ddb panics if under load

[coypu%sdf.org@localhost]

>Number:         52672
>Category:       port-xen
>Synopsis:       'continue' in ddb panics if under load
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Oct 29 17:50:00 +0000 2017
>Originator:     coypu
>Release:        NetBSD 8.99.5
>Organization:
>Environment:
NetBSD lio.xen.prgmr.com 8.99.5 NetBSD 8.99.5 (XEN3_DOMU) #21: Sun Oct 29 17:08:27 UTC 2017  lio%lio.xen.prgmr.com@localhost:/home/lio/obj/sys/arch/amd64/compile/XEN3_DOMU amd64

>Description:
ss          e02b
netbsd:breakpoint+0x5:  leave
db{0}> c  
WARNING: SPL NOT LOWERED ON TRAP EXIT 8 6
fatal asynchronous system trap in supervisor mode
trap type 3 code 0 rip 0xffffffff80206505 cs 0xe030 rflags 0x202 cr2 0x75611aca6020 ilevel 0x8 rsp 0xffffa001c065f800
curlwp 0xffffa00015174460 pid 1765.1 lowest kstack 0xffffa001c065c2c0
panic: trap
cpu0: Begin traceback...
vpanic() at netbsd:vpanic+0x140
snprintf() at netbsd:snprintf
startlwp() at netbsd:startlwp
alltraps() at netbsd:alltraps+0x104
xencons_tty_input() at netbsd:xencons_tty_input+0xb2
xencons_handler() at netbsd:xencons_handler+0x6a
xen_intr_biglock_wrapper() at netbsd:xen_intr_biglock_wrapper+0x1d
evtchn_do_event() at netbsd:evtchn_do_event+0x27e
do_hypervisor_callback() at netbsd:do_hypervisor_callback+0x17a
hypervisor_callback() at netbsd:hypervisor_callback+0xa3
pmap_zero_page() at netbsd:pmap_zero_page+0x197
uvm_pagealloc_strat() at netbsd:uvm_pagealloc_strat+0x513
uvmfault_promote() at netbsd:uvmfault_promote+0x2aa
uvm_fault_internal() at netbsd:uvm_fault_internal+0xc83
trap() at netbsd:trap+0x393
--- trap (number 6) ---
75611c0a8baa:
cpu0: End traceback...

dumping to dev 142,1 (offset=20971519, size=0): not possible
rebooting...


compiling in background (not printing) doesn't seem to change things.
>How-To-Repeat:

>Fix: