On Sat, 26 Aug 2006 14:09:55 -0700 (PDT)
Linus Torvalds <[email protected]> wrote:
> On Fri, 25 Aug 2006, Dave Jones wrote:
> > On Thu, Aug 24, 2006 at 09:17:04AM -0700, Andrew Morton wrote:
> > > We already have sufficient locking primitives to get this right. Let's fix
> > > cpufreq locking rather than introduce complex new primitives which we hope
> > > will work in the presence of the existing mess.
> > >
> > > Step 1: remove all mention of lock_cpu_hotplug() from cpufreq.
> > > Step 2: work out what data needs to be locked, and how.
> > > Step 3: implement.
> > this is what I planned to do weeks ago when this mess first blew up.
> > I even went as far as sending Linus a patch for (1).
> > He seemed really gung-ho about trying to fix up the current mess though,
> > and with each incarnation since, I've been convinced we're making
> > the problem worse rather than really improving anything.
> I definitely want to have this fixed, and Gautham's patches look like a
> good thing to me, but the "trying to fix up the current mess" part was
> really about trying to get 2.6.18 in a mostly working state rather than
> anything else. I think it's been too late to try to actually _fix_ it for
> 2.6.18 for a long time already.
> So my reaction is that this redesign should go in asap after 2.6.18,
> unless people feel strongly that the current locking has so many bugs that
> people can actually _hit_ in practice that it's better to go for the
> redesign early.
It certainly needs a redesign. A new sort of lock which makes it appear to
work won't fix races like:
int cpufreq_update_policy(unsigned int cpu)
struct cpufreq_policy *data = cpufreq_cpu_get(cpu);
I rather doubt that anyone will be hitting the races in practice. I'd
recommend simply removing all the lock_cpu_hotplug() calls for 2.6.18.
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