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[Xen-devel] Re: cpupools and locking

To: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Juergen Gross <juergen.gross@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: cpupools and locking
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 4 May 2010 22:52:46 +0100
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On 04/05/2010 19:51, "George Dunlap" <George.Dunlap@xxxxxxxxxxxxx> wrote:

> Something seems not quite right about the cpupool locking... in
> xen/common/cpupool.c:cpupool_do_domctl(), the cpupool_lock is only
> held during the find for several operations.  Doesn't that mean that,
> for instance, it's possible for someone to call CPUPOOL_OP_DESTROY,
> while someone concurrently calls CPUPOOL_OP_INFO, such that in the
> INFO case, the find succeeds, but the structure is shortly thereafter
> freed by DESTROY, even though INFO code still has a pointer to it
> which may be dereferenced?  I don't see any reference counting... am I
> missing something?

It certainly looks like "optimistic" concurrency control to me. :-)

 -- Keir

>  -George

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