bin/56293: Xen Dom0 with no active DomUs stalls during shutdown

[Hauke Fath <hf%spg.tu-darmstadt.de@localhost>]

>Number:         56293
>Category:       bin
>Synopsis:       Xen Dom0 with no active DomUs stalls during shutdown
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jul 02 11:05:01 +0000 2021
>Originator:     Hauke Fath <hf%spg.tu-darmstadt.de@localhost>
>Release:        NetBSD 9.2_STABLE
>Organization:
Technische Universitaet Darmstadt
>Environment:
	
	
System: NetBSD Unspitze 9.2_STABLE NetBSD 9.2_STABLE (FEUERKOGEL_DOM0-$Revision$) #0: Wed Jun 30 02:13:46 CEST 2021 hf@Hochstuhl:/var/obj/netbsd-builds/9/amd64/sys/arch/amd64/compile/FEUERKOGEL_DOM0 amd64
Architecture: x86_64
Machine: amd64
>Description:

	A Xen Dom0 with no active DomUs and the following rc.conf entries


# XEN support
# switch off when no active DomUs - xenstored busy-loops otherwise
xencommons=NO
xenwatchdog=NO

# XXX An empty, but set $xendomains will hang xl in state D during
# shutdown.

xendomains=" "
                       xendomains_config="/etc/pkg/xen/%s.conf"


	will stall during shutdown, with an attempt at listing the
	domains stuck in kernel land

2145 ?       D<   0:00.02 /usr/pkg/sbin/xl list 


	Commenting out xendomains and xendomains_config rc.conf
	entries does not make a difference.

	At this point, breaking into the debugger on a serial console
	is not possible, and the machine has to be physically
	reset. In times of Covid, this is even more annoying than
	usual.

	
>How-To-Repeat:

	Set up a Xen Dom0, but no DomUs, yet.
	Try to 'shutdown -r now'.
 
	
>Fix:
	Yes, please.

	The Xen related rc.d scripts are a bit of a hairball, which I
	will not venture into. But a plain, innocent 'xl list'
	shouldn't get stuck in the first place.

	

>Unformatted: