Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

Steven Rostedt
2009-01-08T15:30:52Z

On Thu, 8 Jan 2009, Steven Rostedt wrote:
> > > > + /*
> > > > + * We need to validate that we can do a
> > > > + * get_cpu() and that we have the percpu area.
> > > > + */
> > > > + if (!cpu_online(cpu))
> > > > + goto out;
> > >
> > > Should we need to do a "get_cpu" or something? Couldn't the CPU disappear
> > > between these two calls. Or does it do a stop-machine and the preempt
> > > disable will protect us?
> >
> > Did you miss the preempt_disable() a bit up?
>
> No, let me rephrase it better. Does the preempt_disable protect against
> another CPU from going off line? Does taking a CPU off line do a
> stop_machine?

I just looked at the cpu hotplug code, and it does call stop machine. All
is in order ;-)

-- Steve