PERFORCE change 103633 for review

[John Baldwin]

On Friday 11 August 2006 13:20, Robert Watson wrote:
> On Fri, 11 Aug 2006, John Baldwin wrote:
> 
> >> I think the main problem (which is now fixed) was with this:
> >>
> >> 	copyin(addr, val1);
> >> 	if (val1 == val2)
> >> 	   	....
> >>
> >> being non-atomic. On the other hand I tried to use other locks other then 
> >> Giant and it didnt work. I hope to investigate that later. Now I have 
this 
> >> working and my focus is elsewhere.
> >
> > No, what you have done is wrong.  The idea of doing copyin() and then 
> > compare is just plain not going to work. :)  You will need to use
> > casuptr() or the like similar to the umtx code.  This is assuming that a
> > futex can be manipulated from userland w/o entering the kernel.
> 
> I assume that we can basically just do whatever Linux does here for 
> synchronization...

Yes, but my assumption is that it lets the easy cases just run in userland and 
only goes into the kernel for a hard case, so you need to use atomic ops such 
as casuptr().

-- 
John Baldwin