Re: return value of ptep_get_and_clear

[Brian Gerst <bgerst@didntduck.org>]

Kumar Gala wrote:
> ptep_get_and_clear has a signature that looks something like:
>
> static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned 
> long addr,
>                                        pte_t *ptep)
>
> It appears that its suppose to return the pte_t pointed to by ptep 
> before its modified.  Why do we bother doing this?  The caller seems 
> perfectly able to dereference ptep and hold on to it.  Am I missing 
> something here?
>
> If not, I'll work up a set of patches to change ptep_get_and_clear and 
> its callers for post 2.6.12 release.
>
> - kumar

Because it is an atomic operation.  If you dereference it before 
ptep_get_and_clear() it could change in between.

--
				Brian Gerst
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