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

Ming Lei
2019-05-10T03:40:15Z

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().
>
> Fixes: dac56212e8127 ("bio: skip atomic inc/dec of ->bi_cnt for most use cases")
> Cc: stable@vger.kernel.org
> Reported-by: "Paul E. McKenney" <paulmck@linux.ibm.com>
> Reported-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: linux-block@vger.kernel.org
> ---
> include/linux/bio.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index e584673c18814..5becbafb84e8a 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -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();
> + smp_mb();
> }
> atomic_set(&bio->__bi_cnt, count);
> }
> --
> 2.7.4
>

Looks fine,

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming