On Fri, Dec 20, 2013 at 12:37:07PM -0500, Steven Rostedt wrote:
> On Fri, 20 Dec 2013 18:13:43 +0100
> Peter Zijlstra <pet...@infradead.org> wrote:
>
>
> > @@ -4985,6 +4942,23 @@ migration_call(struct notifier_block *nf
> > unsigned long flags;
> > struct rq *rq = cpu_rq(cpu);
> >
> > + switch (action) {
> > + case CPU_DOWN_PREPARE: /* explicitly allow suspend */
> > + {
> > + struct dl_bw *dl_b = dl_bw_of(cpu);
> > + int cpus = dl_bw_cpus(cpu);
> > + bool overflow;
> > +
> > + raw_spin_lock_irqsave(&dl_b->lock, flags);
> > + overflow = __dl_overflow(dl_b, cpus-1, 0, 0);
> > + raw_spin_unlock_irqrestore(&dl_b->lock, flags);
> > +
> > + if (overflow)
> > + return notifier_from_errno(-EBUSY);
>
> Is it possible to have a race here to create a new deadline task that
> may work with cpus but not cpus-1? That is, if a new deadline task is
> currently being created as a CPU is going offline, this check happens
> first while the creation is spinning on the dl_b->lock, and it sets
> overflow to false, then once the lock is released, the new deadline
> task makes the condition true.
>
> Should the system call have a get_online_cpus() somewhere?
No, should be all good; the entire admission control is serialized by
that dl_b->lock, and its a raw_spin_lock (as can be seen from the above)
which already very much excludes hotplug.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
