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Re: [PATCH 2/7] containers (V7): Cpusets hooked into containers [message #10931 is a reply to message #10927] Wed, 07 March 2007 16:12 Go to previous messageGo to previous message
Paul Menage is currently offline  Paul Menage
Messages: 642
Registered: September 2006
Senior Member
On 3/7/07, Srivatsa Vaddagiri <vatsa@in.ibm.com> wrote:
> On Mon, Feb 12, 2007 at 12:15:23AM -0800, menage@google.com wrote:
> > - mutex_lock(&callback_mutex);
> > - list_add(&cs->sibling, &cs->parent->children);
> > + cont->cpuset = cs;
> > + cs->container = cont;
> > number_of_cpusets++;
> > - mutex_unlock(&callback_mutex);
>
> What's the rule to read/write number_of_cpusets? The earlier cpuset code was
> incrementing/decrementing under callback_mutex, but now we aren't. How safe is
> that?

We're still inside manage_mutex, so we guarantee that no-one else is
changing it.

>
> The earlier cpuset code also was reading number_of_cpusets w/o the
> callback_mutex held (atleast in cpuset_zone_allowed_softwall). Is that safe?

Yes, I think so. Unless every memory allocator was to hold a lock for
the duration of alloc_pages(), number_of_cpusets can theoretically be
out of date by the time you're using it. But since the process could
have allocated just before you created the first cpuset and moved it
into that cpuset anywa, it's not really a race (and the consequences
are inconsequential).

Paul
 
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