kern/55092: swap on NFS file panic

[martin%NetBSD.org@localhost]

>Number:         55092
>Category:       kern
>Synopsis:       swap on NFS file panic
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 21 08:30:00 +0000 2020
>Originator:     Martin Husemann
>Release:        NetBSD 9.99.50
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD unpluged.duskware.de 9.99.50 NetBSD 9.99.50 (UNPLUGED) #298: Fri Mar 20 17:13:09 CET 2020 martin%seven-days-to-the-wolves.aprisoft.de@localhost:/work/src/sys/arch/evbarm/compile/UNPLUGED evbarm
Architecture: earm
Machine: evbarm
>Description:

This is a diskless machine, root on NFS, swap to file on NFS.

# swapctl -l
Device      1K-blocks     Used    Avail Capacity  Priority
/swap         1048576        0  1048576     0%    0

It did run a full ATF test when I left it last night, and apparently completed
that (full results where available on the NFS server this morning), but some
time later (or during the nightly run?) paniced strangely:

db> show panic
Panic string: (null)
db> bt
0xd4c6eedc: netbsd:uao_set_swslot+0x10
0xd4c6eef4: netbsd:uvmpd_dropswap+0x58
0xd4c6efac: netbsd:uvm_pageout+0x30c
db> c
panic: Fatal abort
[ 39473.8783146] cpu0: Begin traceback...
[ 39473.8783146] 0xd4c6ecdc: netbsd:db_panic+0x14
[ 39473.8783146] 0xd4c6ecf4: netbsd:vpanic+0x11c
[ 39473.8783146] 0xd4c6ed0c: netbsd:snprintf
[ 39473.8783146] 0xd4c6ed44: netbsd:dab_fatal+0x120
[ 39473.8783146] 0xd4c6ed7c: netbsd:dab_align+0xa4
[ 39473.8783146] 0xd4c6ee4c: netbsd:data_abort_handler+0x2a8
[ 39473.8783146] 0xd4c6eedc: netbsd:address_exception_entry+0x58
[ 39473.8783146] 0xd4c6eef4: netbsd:uvmpd_dropswap+0x58
[ 39473.8783146] 0xd4c6efac: netbsd:uvm_pageout+0x30c
[ 39473.8783146] cpu0: End traceback...
[ 39473.8783146] rebooting...

I have seen the same (but did not capture details) after last weeks test
run, but never before.

>How-To-Repeat:
n/a

>Fix:
n/a