Re: [PATCH 2/5] bio: fix improper use of smp_mb__before_atomic()

[Peter Zijlstra]

On Mon, Apr 29, 2019 at 10:14:58PM +0200, Andrea Parri wrote:
> This barrier only applies to the read-modify-write operations; in
> particular, it does not apply to the atomic_set() primitive.
> 
> Replace the barrier with an smp_mb().

> @@ -224,7 +224,7 @@ static inline void bio_cnt_set(struct bio *bio, unsigned int count)
>  {
>  	if (count != 1) {
>  		bio->bi_flags |= (1 << BIO_REFFED);
> -		smp_mb__before_atomic();

Maybe also add:

		/*
		 * XXX the comment that explain this barrier goes here
		 */
> +		smp_mb();
>  	}
>  	atomic_set(&bio->__bi_cnt, count);
>  }