Re: [PATCH] x86 bitops.h commentary on instruction reordering

[Vladislav Bolkhovitin]

So, is there any way to workaround this problem, i.e. prevent bit 
operations reordering on non-x86 architectures? Some kinds of memory 
barriers?

Vlad

Marcelo Tosatti wrote:
> Hi, 
>
> Back when we were discussing the need for a memory barrier in sync_page(), 
> it came to me (thanks Andrea!) that the bit operations can be perfectly 
> reordered on architectures other than x86. 
>
> I think the commentary on i386 bitops.h is misleading, its worth 
> to note that that these operations are not guaranteed not to be 
> reordered on different architectures. 
>
> clear_bit() already does that:
>
>  * clear_bit() is atomic and may not be reordered.  However, it does
>  * not contain a memory barrier, so if it is used for locking purposes,
>  * you should call smp_mb__before_clear_bit() and/or smp_mb__after_clear_bit()
>  * in order to ensure changes are visible on other processors.
>
> What you think of the following
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