kern/57372: bufq_drain should cause subsequent bufq_put to crash

[campbell+netbsd%mumble.net@localhost]

>Number:         57372
>Category:       kern
>Synopsis:       bufq_drain should cause subsequent bufq_put to crash
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Apr 20 13:15:00 +0000 2023
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
the netbsdk(4) foundation
>Environment:
>Description:
After bufq_drain, it is already forbidden for any additional buffers to be queued on entry to bufq_free -- the latter does KASSERT(bufq_peek(bufq) == NULL).

As an improved diagnostic, bufq_drain should cause any attempt at bufq_put to crash with a similar assertion, so we can diagnose where such buffers are coming from at the moment they are submitted, not retrospectively when it's too late to discover that.
>How-To-Repeat:

>Fix:
Yes, please!