Re: 2.4.18 Preempt Freezeups

On Sun, Mar 17, 2002 at 02:14:14AM +0100, Daniel Phillips wrote:
> 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.

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.

> 
> -- 
> Daniel

-- 
---------------------------------------------------------
Victor Yodaiken 
Finite State Machine Labs: The RTLinux Company.
 www.fsmlabs.com  www.rtlinux.com