6.1 panic during shutdown in sleepq_remove()

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

During shutdown of a 6.1_STABLE/amd64 (from a few months ago) I got the following panic:

uvm_fault(0xfffffe807692c4f0, 0x57c56000, 2) -> e
fatal page fault in supervisor mode
trap type 6 code 2 rip ffffffff80285f6e cs 8 rflags 10202 cr2  57c56fce cpl 8 rsp ffff80004c8feac0
kernel: page fault trap, code=0
Stopped in pid 27731.1 (dovecot) at	netbsd:sleepq_remove+0x21:	movq	%
rdx,118(%rax)
db{0}> bt
sleepq_remove() at netbsd:sleepq_remove+0x21
cv_wakeup_all() at netbsd:cv_wakeup_all+0x4b
pipeclose() at netbsd:pipeclose+0x9e
pipe_close() at netbsd:pipe_close+0x18
closef() at netbsd:closef+0x4a
fd_close() at netbsd:fd_close+0x116
syscall() at netbsd:syscall+0xc4
db{0} > show reg
[...]
rdx	25921e8c
[...]
rax	57c56eb6
[...]

This was after the "Done running shutdown hooks." message  and syslogd exiting.

(The line break between "%" and "rdx,118(%rax)" is real.)