Re: [Xen-devel] xl shutdown --wait "racy"

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Thursday, April 17, 2014, 8:09:39 PM, you wrote:

> George Dunlap writes ("Re: [Xen-devel] xl shutdown --wait "racy""):
>> On Wed, Apr 16, 2014 at 3:13 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 
>> wrote:
>> > It is waiting for the domain to be shutdown (state 's') not for the
>> > domain to be destroyed. So it's doing what it said it would (I
>> > appreciate you might not find this distinction helpful under the
>> > circumstances...)
>> 
>> For any reasonable person's definition of "shutdown", it does *not*
>> wait until it's shutdown.  "In the shutdown state" is not something
>> anyone outside of Xen cares about: what they care about is being able
>> to, for example, start the domain again (or start a domain that
>> depends on resources currently held by the shutting down domain).

> Quite.  I think this is simply a bug and it should wait for the domain
> to be destroyed.

It seems the shutdown is racy in another aspect as well, the code in 
"wait_for_domain_deaths" 
on receiving a event doesn't actually check if it's a event related to the 
domain it should wait for. It only checks a count (1 if you shutdown only one 
domain, nb_domains -1 if you shutdown all).

To be less error prone it should ideally pass an array of domids it needs to 
wait for through to wait_for_domain_deaths and check on it.

> It's IMO a tolerable side-effect if this means that when the domain
> shuts down in a way that causes it to be preserved (ie the daemonic xl
> doesn't reap it) xl shutdown -w gets stuck.  (There should be an
> option to restore the former behaviour but it should not be the
> default.)

> Ideally xl would record something somewhere so that it would know
> what's going on and could make "xl shutdown -w" fail in the default
> case if it's going to wait "forever".

There isn't a generic timeout function that could raise an timeout event
when it is taking too long ?

But i'm running into my all too limited C skills here ..
(passive reading is fairly ok, actively building something somewhat more 
complex 
in a sane way is not :-) )


> Ian.



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