Re: [patch 2/2] fix SMP data race in pagetable setup vs walking

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, May 06, 2008 at 07:53:23AM -0700, Linus Torvalds wrote:
> 
> 
> On Tue, 6 May 2008, Nick Piggin wrote:
> > 
> > Right. As the comment says, the x86 stuff is kind of a "reference"
> > implementation, although if you prefer it isn't there, then I I can
> > easily just make it alpha only.
> 
> If there really was a point in teaching people about 
> "read_barrier_depends()", I'd agree that it's probably good to have it as 
> a reference in the x86 implementation.
> 
> But since alpha is the only one that needs it, and is likely to remain so, 
> it's not like we ever want to copy that code to anything else, and it 
> really is better to make it alpha-only if the code is so much uglier.
> 
> Maybe just a comment?
> 
> As to the ACCESS_ONCE() thing, thinking about it some more, I doubt it 
> really matters. We're never going to change pgd anyway, so who cares if we 
> access it once or a hundred times?

If we are never going to change mm->pgd, then why do we need the
smp_read_barrier_depends()?  Is this handling the initialization
case or some such?

							Thanx, Paul

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