Re: [PATCH 3/5] sbitmap: fix improper use of smp_mb__before_atomic()

Ming Lei
2019-05-10T03:41:15Z

On Mon, Apr 29, 2019 at 10:14:59PM +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: 6c0ca7ae292ad ("sbitmap: fix wakeup hang after sbq resize")
> 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: Omar Sandoval <osandov@fb.com>
> Cc: linux-block@vger.kernel.org
> ---
> lib/sbitmap.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index 155fe38756ecf..4a7fc4915dfc6 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -435,7 +435,7 @@ static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
> * to ensure that the batch size is updated before the wait
> * counts.
> */
> - smp_mb__before_atomic();
> + smp_mb();
> for (i = 0; i < SBQ_WAIT_QUEUES; i++)
> atomic_set(&sbq->ws[i].wait_cnt, 1);
> }
> --
> 2.7.4
>

sbitmap_queue_update_wake_batch() won't be called in fast path, and
the fix is correct too, so:

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

thanks,
Ming