kern/60129: config_detach assertion failure "!dv->dv_detach_done"

["yamt%netbsd.org@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60129
>Category:       kern
>Synopsis:       config_detach assertion failure "!dv->dv_detach_done"
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Mar 25 12:50:00 +0000 2026
>Originator:     YAMAMOTO Takashi
>Release:        -current
>Organization:
	
>Environment:
	
>Description:

	you can easily trigger "!dv->dv_detach_done" assertion failure
	with drvctl.

[  83.8186908] panic: kernel diagnostic assertion "!dv->dv_detach_done" failed: file "/root/git/netbsd-src/sys/kern/subr_autoconf.c", line 3021 fss0
[  83.8186908] cpu1: Begin traceback...
[  83.8186908] vpanic() at netbsd:vpanic+0x189
[  83.8186908] kern_assert() at netbsd:kern_assert+0x4b
[  83.8186908] config_detach() at netbsd:config_detach+0x67
[  83.8186908] drvctl_ioctl() at netbsd:drvctl_ioctl+0x28a
[  83.8186908] sys_ioctl() at netbsd:sys_ioctl+0x1fa
[  83.8186908] syscall() at netbsd:syscall+0x9d
[  83.8186908] --- syscall (number 54) ---
[  83.8186908] netbsd:syscall+0x9d:
[  83.8186908] cpu1: End traceback...

>How-To-Repeat:
	on a qemu/nvmm vm with 2 vcpus:

	while :;do < /dev/vnd0;done & while :;do drvctl -d vnd0;done

	the same symptom with at least fss and cgd.
>Fix:
	eg. stop detaching on close

>Unformatted: