panic: /: bad dir ino null entry

[Bartosz Maciejewski <bartosz%maciejewski.org@localhost>]

Hello,

Does anybody know, how I can solve this problem below? Basically 
suddenly my NetBSD running in PV mode on XCP-NG host started rebooting 
with traceback like this:

Clearing temporary files.
Updating fontconfig cache:[  15.7400601] panic: /: bad dir ino 30113744 
at offset 37896192: null entry

[  15.7400601] cpu0: Begin traceback...
[  15.7400601] vpanic() at netbsd:vpanic+0x143
[  15.7400601] snprintf() at netbsd:snprintf
[  15.7400601] ufs_lookup() at netbsd:ufs_lookup+0x3ba
[  15.7400601] VOP_LOOKUP() at netbsd:VOP_LOOKUP+0x34
[  15.7400601] lookup_once() at netbsd:lookup_once+0x18b
[  15.7400601] namei_tryemulroot() at netbsd:namei_tryemulroot+0x307
[  15.7400601] namei() at netbsd:namei+0x41
[  15.7400601] vn_open() at netbsd:vn_open+0x97
[  15.7400601] do_open() at netbsd:do_open+0x103
[  15.7400601] do_sys_openat() at netbsd:do_sys_openat+0x8b
[  15.7400601] sys_open() at netbsd:sys_open+0x24
[  15.7400601] syscall() at netbsd:syscall+0x9c
[  15.7400601] --- syscall (number 5) ---
[  15.7400601] 6f88f9a42a4a:
[  15.7400601] cpu0: End traceback...

[  15.7400601] dumping to dev 142,1 (offset=2097151, size=0): not possible
[  15.7400601] rebooting...

I detached disks and fsck it but after connecting back to same machine 
everything started again. When I press ctrl+C just right and I cancel 
"Updating fontconfig cache" phase, it boots to login prompt. With trials 
and errors I managed to identify that /var/cache/fontconfig is directory 
that when accessed, ls, du or whatever action I take with it, its 
momentally panic :/

I even created new machine from scratch and tried to rsync everything 
without /var/cache/fontconfig, and after some time, new machine started 
producing same error.

I'm 100% sure all disks in SR of XCP when this VMs are, are without 
errors, even forced checked its raid didn't show any errors.

While searching I stumbled upon something barely fitting my case (I 
can't find it now), that was related to rrdtool producing lots of files. 
I do have on this machine cacti with that I'm feeding with snmp data 
from other machines.

So, any help or pointing to right direction will be helpfull.

System is currently running with NetBSD 9.2_STABLE

uname -a
NetBSD u-dom-fw01 9.2_STABLE NetBSD 9.2_STABLE (XEN3_DOMU) #0: Sat Jul 
17 18:46:27 CEST 2021 
root@u-dom-fw01:/root/sysbuild/amd64/obj/usr/src/sys/arch/amd64/compile/XEN3_DOMU 
amd64