nfs mount causes panic when server disappears

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

I'm nfs mounting some file systems from a Synology NAS on
NetBSD-7.99.1/amd64 from Oct 20.

The fstab entries look like this:

192.168.1.2:/volume1/music      /disk/music     nfs     intr,nodev,nosuid,rw,soft,tcp

I have had it happen at least two times already that I rebooted the
NAS (for updates) and tried accessing the file system later, just to
get a kernel panic.

fatal page fault in supervisor mode
trap type 6 code 0 rip ffffffff80265095 cs 8 rflags 10202 cr2 ffff8003393c8000 ilevel 4 rsp fffffe813a44aaa8
curlwp 0xfffffe882df2d420 pid 0.3 lowest kstack 0xfffffe813a4472c0
panic: trap
cpu0: Begin traceback...
vpanic() at netbsd:vpanic+0x13c
snprintf() at netbsd:snprintf
startlwp() at netbsd:startlwp
cpu0: End traceback...

I have crash dumps. The latest one is unusable:
(gdb) target kvm netbsd.core
<unavailable> in ?? ()
(gdb) bt
#0  <unavailable> in ?? ()
Backtrace stopped: not enough registers or memory available to unwind further

Same for the one before that.
I'm just doing

gzcat /var/crash/netbsd.XX.gz > netbsd
gzcat /var/crash/netbsd.XX.core.gz > netbsd.core
gdb netbsd
> target kvm netbsd.core
> bt

so I have to assume something's broken with kernel core dumps (at
least for me, in this situation).
 Thomas