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

[Nick Piggin <npiggin@suse.de>]

On Tue, May 13, 2008 at 08:45:51AM -0700, Linus Torvalds wrote:
> 
> 
> On Tue, 13 May 2008, Nick Piggin wrote:
> > 
> > No, *everyone* (except arch-only non-alpha developer) needs to know about
> > it.
> 
> Umm. In architecture files, by definition, only alpha needs to know about 
> it.
> 
> That was very much an architecture-specific file: we're talking about 
> asm-x86/pgtable_32.h here.
> 
> > x86 especially is a reference and often is a proving ground for code that
> > becomes generic, so I'd say even x86 developers should need to know about
> > it too.
> 
> And in reference files that are architecture-specific, there is absolutely 
> *no point* in ever having read_barrier_depends(). Because even if another 
> architecture copies it, it's better off without it.

Uh, I don't follow your logic. The "reference" Linux memory model
requires it, so I don't see how you can justify saying it is wrong
just because a *specific* architecture doesn't need it.

I think that regardless of whether it is required or not, it is good
to have in order to prompt the reader to think about memory ordering.
I also think it is a good idea to use smp_rmb/smp_wmb in x86 only
code even though that is a noop too.

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