Re: cpupools and locking

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 05/04/2010 08:51 PM, George Dunlap 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?

cpupool_do_domctl is called always while the domctl lock is being held. Maybe
I should have added a comment to document this assumption.

Keir's patch to move the cpupool commands to the sysctl interface makes a
change of the locking mandatory. I'll setup a patch for this.


Juergen

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Juergen Gross                 Principal Developer Operating Systems
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