On Tue, 2007-05-29 at 13:56 -0700, Linus Torvalds wrote:
>
> On Mon, 28 May 2007, Srivatsa Vaddagiri wrote:
> >
> > So is it settled now on what approach we are going to follow (freezer
> > vs lock based) for cpu hotplug? I thought that Linus was not favouring
> > freezer
> > based approach sometime back ..
>
> As far as I'm concerned, we should
> - use "preempt_disable()" to protect against CPU's coming and going
> - use "stop_machine()" or similar that already honors preemption, and
> which I trust a whole lot more than freezer.
> - .. especially since this is already how we are supposed to be protected
> against CPU's going away, and we've already started doing that (for an
> example of this, see things like e18f3ffb9c from Andrew)
Indeed, this is how it was supposed to work.
Note that it is possible to make stop_machine() an even larger hammer,
by scheduler mods to flush all the preempted tasks. This would drop the
requirement for preempt_disable().
But cute as that would be, I've been waiting until someone demonstrates
an actual need...
Rusty.
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