On Thu, 23 Jun 2011, Peter Zijlstra wrote:
> On Wed, 2011-06-22 at 15:20 -0700, Suresh Siddha wrote:
> > +#ifdef CONFIG_SMP
> > + /*
> > + * If we are not yet online, then there can be no stop_machine() in
> > + * parallel. Stop machine ensures this by using get_online_cpus().
> > + *
> > + * If we are online, then we need to prevent a stop_machine()
> > happening
> > + * in parallel by taking the stop cpus mutex.
> > + */
> > + if (cpu_online(raw_smp_processor_id()))
> > + mutex_lock(&stop_cpus_mutex);
> > +#endif
>
> This reads like an optimization, is it really worth-while to not take
> the mutex in the rare offline case?
You cannot block on a mutex when you are not online, in fact you
cannot block on it when not active, so the check is wrong anyway.
Thanks,
tglx
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