Re: port-xen/50659: Xen4.5 crash with vnds

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Wed, Mar 23, 2016 at 02:05:01AM +0000, Robert Elz wrote:
> The following reply was made to PR kern/50659; it has been noted by GNATS.
> 
> From: Robert Elz <kre%munnari.OZ.AU@localhost>
> To: gnats-bugs%NetBSD.org@localhost
> Cc: 
> Subject: Re: port-xen/50659: Xen4.5 crash with vnds
> Date: Wed, 23 Mar 2016 09:01:42 +0700
> 
>      Date:        Wed, 23 Mar 2016 00:35:01 +0000 (UTC)
>      From:        mlelstv%serpens.de@localhost (Michael van Elst)
>      Message-ID:  <20160323003501.606657ACB7%mollari.NetBSD.org@localhost>
>  
>    |  The EBUSY comes from specfs that prevents opening a block device twice.
>  
>  Ah, OK, thanks - so this is not a problem with vnd at all, and is a Xen
>  script (lack of locking or something) or user error?

I think it is Xen's problem.
I noticed that xen 4.5 starts domUs concurently (/etc/rc.d/xendomains start)
which prevented be from upgrading to 4.5 because of concurency problems
in my network scripts (local change).

Now if it runs scripts for each block device (or, I guess, each
network device) in parallel, then we have a problem.
Adding a simple locking in the shell script may not be enough:
I tried this for my network script, but then xl start times out
on the script :(
We may need something better than shlock(1)

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--