Re: [PATCH] locking/atomic: atomic: Use arch_atomic_{read,set} in generic atomic ops

[Peter Zijlstra]

On Thu, Jan 26, 2023 at 06:33:54PM +0100, Jules Maselbas wrote:

> @@ -58,9 +61,11 @@ static inline int generic_atomic_fetch_##op(int i, atomic_t *v)		\
>  static inline void generic_atomic_##op(int i, atomic_t *v)		\
>  {									\
>  	unsigned long flags;						\
> +	int c;								\
>  									\
>  	raw_local_irq_save(flags);					\
> -	v->counter = v->counter c_op i;					\
> +	c = arch_atomic_read(v);					\
> +	arch_atomic_set(v, c c_op i);					\
>  	raw_local_irq_restore(flags);					\
>  }

This and the others like it are a bit sad, it explicitly dis-allows the
compiler from using memops and forces a load-store.

The alternative is writing it like:

	*(volatile int *)&v->counter c_op i;

but that's pretty shit too I suppose.