Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transactionabstraction

[Linus Torvalds]

On Thu, 19 Jun 2008, Ingo Molnar wrote:
> 
> Below is the commit, it needed a small amount of massaging to apply the 
> void * -> unsigned long * change in the x86/bitops topic.

Well, that's your bug right there.

The macros very much depended on the pointers being "void *", due to the 
pointer arithmetic (which is a gcc extension that we use extensively - 
"void *" arithmetic works as if it was a byte pointer).

When you changed "addr" to "volatile unsigned long *", now the arithmetic 
ended up multiplying the offset by the size of "long" before adding it.

That said, the _original_ patch wasn't tested either, but quite frankly, 
looking over the patch one more time, I can't really see how it could 
break.

		Linus
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