K 10
svn:author
V 3
avg
K 8
svn:date
V 27
2021-05-21T10:32:34.821752Z
K 7
svn:log
V 902
PCI hot-plug: use dedicated taskqueue for device attach / detach

Attaching and detaching devices can be heavy-weight and detaching can
sleep waiting for events.  For that reason using the system-wide
single-threaded taskqueue_thread is not really appropriate.
There is even a possibility for a deadlock if taskqueue_thread is used
for detaching.

In fact, there is an easy to reproduce deadlock involving nvme, pass
and a sudden removal of an NVMe device.
A pass peripheral would not release a reference on an nvme sim until
pass_shutdown_kqueue() is executed via taskqueue_thread.  But the
taskqueue's thread is blocked in nvme_detach() -> ... -> cam_sim_free()
because of the outstanding reference.

Sponsored by:	CyberSecure
Reviewed by:	mav, imp

(cherry picked from commit 12588ce02dd835b332952d9fece5881d943554a9)

Git Hash:   2def2de60a6d0b979964bb67c5ff0e24d098e4a9
Git Author: avg@FreeBSD.org
END