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SubjectRe: [PATCH v2] buffer: Fix I/O error due to ARM read-after-read hazard
On Thu, Nov 14, 2019 at 09:28:48PM +0800, Herbert Xu wrote:
> Will Deacon <will@kernel.org> wrote:
> >
> > which is what can happen due to this erratum. It's generally good practice
> > to use READ_ONCE() when reading something which can be updated concurrently
> > because:
> >
> > * It ensures that the value is (re-)loaded from memory
> >
> > * It prevents the compiler from performing harmful optimisations,
> > such as merging or tearing (although in this case I suspect
> > these are ok because we're dealing with a single bit)
> >
> > * On Alpha, it gives you a barrier so that dependency ordering
> > can be relied upon from the load
>
> The Alpha barrier matters for pointers, how could it make a
> difference for individual bits?

I guess you could use the result of test_bit to index into an array or
something?

Will

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