Re: [PATCH for-next] RDMA/rxe: Fix memory ordering problem for resize cq

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On Wed, May 26, 2021 at 6:27 AM Bob Pearson <rpearsonhpe@xxxxxxxxx> wrote:
>
> The rxe driver has recently begun exhibiting failures in the python
> tests that are due to stale values read from the completion queue
> producer or consumer indices. Unlike the other loads of these shared
> indices those in queue_count() were not protected by smp_load_acquire().
>
> This patch replaces loads by smp_load_acquire() in queue_count().
> The observed errors no longer occur.
>
> Reported-by: Zhu Yanjun <zyj2020@xxxxxxxxx>

My email address is wrong. It should be zyjzyj2000@xxxxxxxxx

Zhu Yanjun

> Fixes: d21a1240f516 ("RDMA/rxe: Use acquire/release for memory ordering")
> Signed-off-by: Bob Pearson <rpearsonhpe@xxxxxxxxx>
> ---
>  drivers/infiniband/sw/rxe/rxe_queue.h | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/sw/rxe/rxe_queue.h b/drivers/infiniband/sw/rxe/rxe_queue.h
> index 2902ca7b288c..5cb142282fa6 100644
> --- a/drivers/infiniband/sw/rxe/rxe_queue.h
> +++ b/drivers/infiniband/sw/rxe/rxe_queue.h
> @@ -161,8 +161,22 @@ static inline unsigned int index_from_addr(const struct rxe_queue *q,
>
>  static inline unsigned int queue_count(const struct rxe_queue *q)
>  {
> -       return (q->buf->producer_index - q->buf->consumer_index)
> -               & q->index_mask;
> +       u32 prod;
> +       u32 cons;
> +       u32 count;
> +
> +       /* make sure all changes to queue complete before
> +        * changing producer index
> +        */
> +       prod = smp_load_acquire(&q->buf->producer_index);
> +
> +       /* make sure all changes to queue complete before
> +        * changing consumer index
> +        */
> +       cons = smp_load_acquire(&q->buf->consumer_index);
> +       count = (prod - cons) % q->index_mask;
> +
> +       return count;
>  }
>
>  static inline void *queue_head(struct rxe_queue *q)
> --
> 2.30.2
>



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