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SubjectRe: 2.4.18 Preempt Freezeups
Date
On March 17, 2002 02:54 am, yodaiken@fsmlabs.com wrote:
> On Sun, Mar 17, 2002 at 02:14:14AM +0100, Daniel Phillips wrote:
> > On March 17, 2002 02:13 am, yodaiken@fsmlabs.com wrote:
> > > On Sun, Mar 17, 2002 at 01:33:04AM +0100, Daniel Phillips wrote:
> > > > On March 16, 2002 01:40 am, yodaiken@fsmlabs.com wrote:
> > > > >
> > > > > Without preempt:
> > > > > x = movefrom processor register;
> > > // if preemption is on, we can be preempted and restart
> > > // on another processor so x will be wrong
> > > > > do_something with x
> > > > >
> > > > > is safe in SMP
> > > > > With [preempt] it requires a lock.
> > > >
> > > > It must be a trick question. Why would it?
> > >
> > > See comment.
> >
> > Which processor register were you thinking of? Surely not anything in the
> > general register set, and otherwise, it's just another example of per-cpu
> > data. It needs to be protected, and the protection is lightweight.
>
> So what didn't you understand? Your (dubious)
> assertion that the lock is "lightweight"
> has absolutely no bearing on whether a lock is needed or not.

I didn't understand which kind of register you meant (because you didn't say).
For the bog-standard variety I don't see a problem.

Protection of special registers is lightweight, it's just a preempt
disable/enable (inc/dec).

--
Daniel
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