Re: [patch V4 part 1 06/36] compiler: Simple READ/WRITE_ONCE() implementations

Will Deacon
2020-05-06T13:33:41Z

On Tue, May 05, 2020 at 03:16:08PM +0200, Thomas Gleixner wrote:
> READ/WRITE_ONCE_NOCHECK() is required for atomics in code which cannot be
> instrumented like the x86 int3 text poke code. As READ/WRITE_ONCE() is
> undergoing a rewrite, provide __{READ,WRITE}_ONCE_SCALAR().
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> include/linux/compiler.h | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -313,6 +313,14 @@ unsigned long read_word_at_a_time(const
> __u.__val; \
> })
>
> +#define __READ_ONCE_SCALAR(x) \
> + (*(const volatile typeof(x) *)&(x))
> +
> +#define __WRITE_ONCE_SCALAR(x, val) \
> +do { \
> + *(volatile typeof(x) *)&(x) = val; \
> +} while (0)

FWIW, these end up being called __READ_ONCE() and __WRITE_ONCE() after
the rewrite; the *_SCALAR() variants will call into kcsan_check_atomic_*().

If you go with that naming now, then any later conflict should fall out in
the wash.

Will