Re: Bulk CPU Hotplug (Was Re: [PATCH] Do not force shutdown/reboot to boot cpu.)

[Robin Holt <holt@sgi.com>]

On Sat, Apr 13, 2013 at 06:30:22PM +0200, Oleg Nesterov wrote:
> On 04/12, Robin Holt wrote:
> >
> > +void migrate_to_boot_cpu(void)
> > +{
> > +	/* The boot cpu is always logical cpu 0 */
> > +	int reboot_cpu_id = 0;
> > +
> > +	/* Make certain the cpu I'm about to reboot on is online */
> > +	if (!cpu_online(reboot_cpu_id))
> > +		reboot_cpu_id = smp_processor_id();
> > +
> > +	/* Make certain I only run on the appropriate processor */
> > +	set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));
> 
> This is only theoretical, but perhaps it makes sense to set
> PF_THREAD_BOUND before set_cpus_allowed_ptr() ? To prevent the
> race with another thread doing sched_setaffinity().

I don't quite understand this comment.  We are migrating our own thread.
How does setting PF_THREAD_BOUND have any effect?

Robin