Re: 2.4.18 Preempt Freezeups

[Daniel Phillips]

On March 17, 2002 02:13 am, [e-mail] wrote:
> On Sun, Mar 17, 2002 at 01:33:04AM +0100, Daniel Phillips wrote:
> > On March 16, 2002 01:40 am, [e-mail] 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.

-- 
Daniel