panic: softint screwup

[Jared McNeill <jmcneill%invisible.ca@localhost>]

First time seeing this one.. an arm64 board sitting idle at the login 
prompt rebooted itself with this panic. Unfortunately the default 
ddb.onpanic=0 strikes again and I can't get any more information than 
this:

[ 364.3342263] curcpu=0, spl=4 curspl=7
[ 364.3342263] onproc=0xffff00237f743080 => l_stat=7 l_flag=20000201 l_cpu=0
[ 364.3342263] curlwp=0xffff00237f71e580 => l_stat=1 l_flag=00000200 l_cpu=0
[ 364.3342263] pinned=0xffff00237f71e100 => l_stat=7 l_flag=00000200 l_cpu=0
[ 364.3342263] panic: softint screwup
[ 364.3342263] cpu0: Begin traceback...
[ 364.3342263] trace fp ffffffc101da7be0
[ 364.3342263] fp ffffffc101da7c00 vpanic() at ffffffc0004ad728 netbsd:vpanic+0x160
[ 364.3342263] fp ffffffc101da7c70 panic() at ffffffc0004ad81c netbsd:panic+0x44
[ 364.3342263] fp ffffffc101da7d40 softint_dispatch() at ffffffc00047bda4 netbsd:softint_dispatch+0x5c4
[ 364.3342263] fp ffffffc101d9fc30 cpu_switchto_softint() at ffffffc000085198 netbsd:cpu_switchto_softint+0x68
[ 364.3342263] fp ffffffc101d9fc80 splx() at ffffffc0000040d4 netbsd:splx+0xbc
[ 364.3342263] fp ffffffc101d9fcb0 callout_softclock() at ffffffc000489e04 netbsd:callout_softclock+0x36c
[ 364.3342263] fp ffffffc101d9fd40 softint_dispatch() at ffffffc00047b8dc netbsd:softint_dispatch+0xfc
[ 364.3342263] fp ffffffc101d3fcc0 cpu_switchto_softint() at ffffffc000085198 netbsd:cpu_switchto_softint+0x68
[ 364.3342263] fp ffffffc101d3fdf8 cpu_idle() at ffffffc000086128 netbsd:cpu_idle+0x58
[ 364.3342263] fp ffffffc101d3fe40 idle_loop() at ffffffc0004546a4 netbsd:idle_loop+0x174
address 0x100 is invalid
address 0xe8 is invalid
[ 364.3342263] cpu0: End traceback...

[ 364.3342263] dump to dev 92,33 not possible
[ 364.3342263] rebooting...