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SubjectRe: [patch] cpusets: allow PF_THREAD_BOUND kworkers to escape from a cpuset
Hello,

Sorry about the delay. I'm mostly offline until the end of this
month.

On Fri, Sep 23, 2011 at 01:20:51PM -0700, David Rientjes wrote:
> > @@ -1382,9 +1383,10 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
> > * set of allowed nodes is unnecessary. Thus, cpusets are not
> > * applicable for such threads. This prevents checking for success of
> > * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
> > - * be changed.
> > + * be changed. We also disallow attaching kthreadd, to prevent it's
> > + * child from becoming trapped should it then acquire PF_THREAD_BOUND.
> > */
> > - if (tsk->flags & PF_THREAD_BOUND)
> > + if (tsk->flags & PF_THREAD_BOUND || tsk == kthreadd_task)
> > return -EINVAL;
> >
> > return 0;
>
> I like this much better, let's wait to hear from Tejun because he may
> shead some light on whether PF_THREAD_BOUND is really necessary for
> kworkers at all times.

Yes, PF_THREAD_BOUND is necessary. The whole thing depends heavily on
per-cpu behavior. In addition, I don't think it makes much sense to
put kworkers into a cpuset (or any other resource container) which
isn't global to the system. If certain CPU intensive tasks require
scheduler based resource limitation, the RTTD would be creating a
dedicated worker thread for it and put restrictions on that specific
kthread.

Putting kthreadd into a sub cpuset and thus putting restrictions on
random kthreads seems like asking for trouble. So, I agree with the
suggested approach.

Thank you.

--
tejun


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