kern/57849: panic running git on NetBSD src repo

[rbranco%suse.de@localhost]

>Number:         57849
>Category:       kern
>Synopsis:       panic running git on NetBSD src repo
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jan 14 13:00:00 +0000 2024
>Originator:     Ricardo Branco
>Release:        NetBSD 10.0_RC2
>Organization:
>Environment:
NetBSD netbsd.fritz.box 10.0_RC2 NetBSD 10.0_RC2 (CUSTOM) amd64

QEMU VM with 4 vCPU & 8G RAM + 4G swap
>Description:
I compiled my own kernel (git commit 7dfbb8d9be77ef7d8c252379041a4861371dc9fe) without any modifications and I'm getting this error when switching from the netbsd-10 to the trunk branch

$ git checkout netbsd-10
error: unable to unlink old 'external/bsd/file/dist/magic/magdir/tplink': Operation not permitted
error: unable to unlink old 'external/bsd/file/dist/tests/pgp-binary-key-v2-phil.result': No such file or directory
error: unable to unlink old 'external/bsd/file/dist/tests/pgp-binary-key-v3-lutz.result': No such file or directory
error: unable to unlink old 'external/bsd/file/dist/tests/pgp-binary-key-v4-dsa.result': No such file or directory
error: unable to unlink old 'external/bsd/libpcap/dist/pcap-bpf.c': No such file or directory
>How-To-Repeat:
If I clone the netbsd-10 branch and try to checkout trunk I get a panic instead:


[    40.155906] panic: ufsdirhash_findfree: free mismatch
[    40.155906] cpu0: Begin traceback...
[    40.155906] vpanic() at netbsd:vpanic+0x18c
[    40.155906] panic() at netbsd:panic+0x3c
[    40.155906] ufsdirhash_findfree() at netbsd:ufsdirhash_findfree+0x251
[    40.155906] ufs_lookup() at netbsd:ufs_lookup+0x5b9
[    40.166360] VOP_LOOKUP() at netbsd:VOP_LOOKUP+0x3d
[    40.166360] lookup_once() at netbsd:lookup_once+0x1bb
[    40.166360] namei_tryemulroot.constprop.0() at netbsd:namei_tryemulroot.constprop.0+0x37c
[    40.166360] namei() at netbsd:namei+0x43
[    40.166360] vn_open() at netbsd:vn_open+0xf8
[    40.177115] do_open() at netbsd:do_open+0xcc
[    40.177115] do_sys_openat() at netbsd:do_sys_openat+0x74
[    40.177115] sys_open() at netbsd:sys_open+0x24
[    40.177115] syscall() at netbsd:syscall+0x205
[    40.177115] --- syscall (number 5) ---
[    40.187382] netbsd:syscall+0x205:
[    40.187382] cpu0: End traceback...

[    40.187382] dumping to dev 168,1 (offset=8, size=2097022):
[    40.187382] dump WARNING: negative runtime; monotonic clock has gone backwards

>Fix: