Re: [Xen-devel] [PATCH] cpupools: retry cpupool-destroy if domain in cpupool is dying

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.05.14 at 11:56, <juergen.gross@xxxxxxxxxxxxxx> wrote:
> On 14.05.2014 11:16, George Dunlap wrote:
>> On Mon, May 12, 2014 at 12:49 PM, Juergen Gross
>> <juergen.gross@xxxxxxxxxxxxxx> wrote:
>>> When a cpupool is destroyed just after the last domain has been stopped the
>>> domain might already be removed from the domain list without being removed
>>> from the cpupool.
>>> It is easy to detect this situation and to return EAGAIN in this case which
>>> is already handled in libxc by doing a retry.
>>
>> OK, I hate to be picky over two lines, but it still seems to me like
>> this is papering over issues instead of dealing with them properly.
>> The real problem here is that "for_each_domain_in_cpupool()" doesn't
>> actually go over every domain in the cpupool.  Instead of making it so
>> that it actually does, you're compensating for that fact in an ad-hoc
>> fashion.
>>
>> Now as it happens, it looks like all the other current uses of
>> for_each_domain_in_cpupool() work just fine if there are domains in
>> the pool it doesn't see, as long as they're about to disappear.  But
>> we've already seen a bug caused because of a situation where "don't
>> see domains that are about to disappear" *does* actually cause a
>> problem; working around it is just setting a trap for future
>> developers to fall into.  (And who knows, there may already be a bug
>> we haven't discovered in the other invocations of
>> for_each_domain_in_cpupool()).
> 
> This isn't unique to for_each_domain_in_cpupool(). It is a problem for all
> uses of for_each_domain() which are related to resources freed only in
> complete_domain_destroy().

Of which there shouldn't be that many, if any at all.

What prevents cpupool_rm_domain() getting moved from
complete_domain_destroy() to domain_destroy(), before the
domain gets taken off the list? I actually assume that there are
more things here that may not really need deferring until the
last possible moment...

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel