kern/57728: panic: unmount: dangling vnode

[spz%NetBSD.org@localhost]

>Number:         57728
>Category:       kern
>Synopsis:       panic: unmount: dangling vnode
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Nov 27 18:15:00 +0000 2023
>Originator:     S.P.Zeidler
>Release:        NetBSD 10.0_RC1 20231126 (kernel) 20231109 (userland)
>Organization:
	The NetBSD Foundation
>Environment:
System: NetBSD shadow.netbsd.org 10.0_RC1 NetBSD 10.0_RC1 (SHADOW) #2: Sun Nov 26 11:12:23 UTC 2023 spz%franklin.NetBSD.org@localhost:/home/netbsd/10/amd64/obj/sys/arch/amd64/compile/SHADOW amd64
Architecture: x86_64
Machine: amd64
>Description:
[ 107247.8359207] panic: unmount: dangling vnode
[ 107247.8459013] cpu33: Begin traceback...
[ 107247.8459013] vpanic() at netbsd:vpanic+0x183
[ 107247.8558802] panic() at netbsd:panic+0x3c
[ 107247.8558802] dounmount() at netbsd:dounmount+0x23e
[ 107247.8658801] sys_unmount() at netbsd:sys_unmount+0xf8
[ 107247.8658801] syscall() at netbsd:syscall+0x211
[ 107247.8758804] --- syscall (number 22) ---
[ 107247.8758804] netbsd:syscall+0x211:
[ 107247.8758804] cpu33: End traceback...
[ 107247.8858816] fatal breakpoint trap in supervisor mode
[ 107247.8858816] trap type 1 code 0 rip 0xffffffff80235385 cs 0x8 rflags 0x202 cr2 0x73ad797769b5 ilevel 0 rsp 0xffffdf84eb2d5df0
[ 107247.8958813] curlwp 0xffffc2be3eedcb40 pid 6020.6020 lowest kstack 0xffffdf84eb2d12c0
Stopped in pid 6020.6020 (umount) at    netbsd:breakpoint+0x5:  leave
breakpoint() at netbsd:breakpoint+0x5
vpanic() at netbsd:vpanic+0x183
panic() at netbsd:panic+0x3c
dounmount() at netbsd:dounmount+0x23e
sys_unmount() at netbsd:sys_unmount+0xf8
syscall() at netbsd:syscall+0x211
--- syscall (number 22) ---
netbsd:syscall+0x211:
ds          8
es          21
fs          180
gs          5da0
rdi         0
rsi         2da
rbp         ffffdf84eb2d5df0
rbx         0
rdx         1
rcx         ffffffffffffff
rax         800000000000000
r8          0
r9          0
r10         73
r11         fffffffd
r12         ffffffff80c4bbba    ostype+0x9f121
r13         ffffdf84eb2d5e38
r14         104
r15         ffffc2be34206000
rip         ffffffff80235385    breakpoint+0x5
cs          8
rflags      202
rsp         ffffdf84eb2d5df0
ss          10
netbsd:breakpoint+0x5:  leave

	likely while umounting a chroot, i.e. nullmounts, tmpfs, procfs, ptyfs
>How-To-Repeat:
	It's the first occurrence.
>Fix: