Re: [PATCH v2] buffer: Fix I/O error due to ARM read-after-read hazard

[Will Deacon]

On Thu, Nov 14, 2019 at 09:28:48PM +0800, Herbert Xu wrote:
> Will Deacon <will@xxxxxxxxxx> 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