Re: [PATCH] make atomic_t volatile on all architectures

[Jesper Juhl]

On 09/08/2007, Chris Snook <csnook@xxxxxxxxxx> wrote:
> From: Chris Snook <csnook@xxxxxxxxxx>
>
> Some architectures currently do not declare the contents of an atomic_t to be
> volatile.  This causes confusion since atomic_read() might not actually read
> anything if an optimizing compiler re-uses a value stored in a register, which
> can break code that loops until something external changes the value of an
> atomic_t.  Avoiding such bugs requires using barrier(), which causes re-loads
> of all registers used in the loop, thus hurting performance instead of helping
> it, particularly on architectures where it's unnecessary.  Since we generally
> want to re-read the contents of an atomic variable on every access anyway,
> let's standardize the behavior across all architectures and avoid the
> performance and correctness problems of requiring the use of barrier() in
> loops that expect atomic_t variables to change externally.  This is relevant
> even on non-smp architectures, since drivers may use atomic operations in
> interrupt handlers.
>
> Signed-off-by: Chris Snook <csnook@xxxxxxxxxx>
>

Hmm, I thought we were trying to move away from volatile since it is
very weakly defined and towards explicit barriers and locks...
Points to --> Documentation/volatile-considered-harmful.txt


-- 
Jesper Juhl <jesper.juhl@xxxxxxxxx>
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