kern/56614: kernel panic on tmux

[Manuel.Bouyer%lip6.fr@localhost]

>Number:         56614
>Category:       kern
>Synopsis:       kernel panic on tmux
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jan 11 08:20:00 +0000 2022
>Originator:     Manuel Bouyer
>Release:        NetBSD 9.99.93
>Organization:
>Environment:
System: NetBSD comore 9.99.93 NetBSD 9.99.93 (XEN3_DOMU) #11: Tue Jan 11 09:02:24 CET 2022  bouyer@bip:/dsk/l1/misc/bouyer/tmp/amd64/obj/dsk/l1/misc/bouyer/HEAD/clean/src/sys/arch/amd64/compile/XEN3_DOMU amd64
Architecture: x86_64
Machine: amd64
>Description:
	With a -HEAD kernel, running a netbsd-9 userland, I get a panic
	when starting tmux:
[ 140.3443697] uvm_fault(0xffffb900020b28b8, 0x0, 1) -> e
[ 140.3443697] fatal page fault in supervisor mode
[ 140.3443697] trap type 6 code 0 rip 0xffffffff80238b80 cs 0xe030 rflags 0x10202 cr2 0x310 ilevel 0 rsp 0xffffb9003c0d4a48
[ 140.3443697] curlwp 0xffffb90001a800c0 pid 1098.1098 lowest kstack 0xffffb9003c0d02c0
kernel: page fault trap, code=0
Stopped in pid 1098.1098 (tmux) at      netbsd:rw_enter+0x40:   movq    0(%rdi),
%rax
rw_enter() at netbsd:rw_enter+0x40
VOP_READDIR() at netbsd:VOP_READDIR+0x46
vn_readdir() at netbsd:vn_readdir+0xe8
sys___getdents30() at netbsd:sys___getdents30+0x72
syscall() at netbsd:syscall+0x9c
--- syscall (number 390) ---

	A forced fsck doesn't find any filesystem issue.
	This didn't happen with a kernel from a few days ago (thurday or
	friday last week).

>How-To-Repeat:
	boot a -HEAD kernel on a -9 userland, start a new tmux session
>Fix: