Re: [PATCH rdma-next] RDMA/mlx5: Free software WCs left on wc_list at CQ destroy

[Leon Romanovsky <leon@kernel.org>]

On Tue, Nov 03, 2026 at 06:55:19PM +0200, Edward Srouji wrote:
> Software WCs generated by mlx5_ib_generate_wc() are allocated one at a
> time and linked onto cq->wc_list. The only thing that ever frees them is
> poll_soft_wc(), i.e. a consumer actually reaping them. If the CQ is
> destroyed while entries are still linked, those allocations are leaked.

Is this real issue? Just put WARN_ON(!list_empty(...)) instead.

Thanks

> 
> Drain the list in destroy_cq_kernel(). Nothing can be walking wc_list by
> then: the poll context is the only walker, notify_work the only thing
> that can re-arm it, and both are stopped before post_destroy_cq() runs.
> 
> destroy_cq_kernel() is also the error unwind for mlx5_ib_create_cq(), so
> move the INIT_LIST_HEAD() of wc_list up next to the other list
> initialisations, ahead of anything that can jump to err_cqb.  The driver
> object is zero-allocated, and list_for_each_entry_safe() evaluates the
> next linkage before testing the loop condition, so draining a wc_list
> that is still all zeroes would oops.
> 
> Fixes: 25361e02c448 ("IB/mlx5: Generate completions in software")
> Reviewed-by: Maher Sanalla <msanalla@nvidia.com>
> Signed-off-by: Edward Srouji <edwards@nvidia.com>
> ---
>  drivers/infiniband/hw/mlx5/cq.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/hw/mlx5/cq.c b/drivers/infiniband/hw/mlx5/cq.c
> index 55ffd7d4de517e6ce3f04c98b4edcd94b12e43b3..2f7ac350c3d8f179ad1d4d8c1181b93f3151c7ce 100644
> --- a/drivers/infiniband/hw/mlx5/cq.c
> +++ b/drivers/infiniband/hw/mlx5/cq.c
> @@ -933,8 +933,19 @@ static int create_cq_kernel(struct mlx5_ib_dev *dev, struct mlx5_ib_cq *cq,
>  	return err;
>  }
>  
> +static void drain_soft_wc(struct mlx5_ib_cq *cq)
> +{
> +	struct mlx5_ib_wc *soft_wc, *next;
> +
> +	list_for_each_entry_safe(soft_wc, next, &cq->wc_list, list) {
> +		list_del(&soft_wc->list);
> +		kfree(soft_wc);
> +	}
> +}
> +
>  static void destroy_cq_kernel(struct mlx5_ib_dev *dev, struct mlx5_ib_cq *cq)
>  {
> +	drain_soft_wc(cq);
>  	free_cq_buf(dev, &cq->buf);
>  	mlx5_db_free(dev->mdev, &cq->db);
>  }
> @@ -1067,6 +1078,7 @@ int mlx5_ib_create_cq(struct ib_cq *ibcq, const struct ib_cq_init_attr *attr,
>  	spin_lock_init(&cq->lock);
>  	INIT_LIST_HEAD(&cq->list_send_qp);
>  	INIT_LIST_HEAD(&cq->list_recv_qp);
> +	INIT_LIST_HEAD(&cq->wc_list);
>  
>  	cqe_size = cache_line_size() == 128 ? 128 : 64;
>  	err = create_cq_kernel(dev, cq, entries, cqe_size, &cqb, &index,
> @@ -1102,7 +1114,6 @@ int mlx5_ib_create_cq(struct ib_cq *ibcq, const struct ib_cq_init_attr *attr,
>  	mlx5_ib_dbg(dev, "cqn 0x%x\n", cq->mcq.cqn);
>  	cq->mcq.event = mlx5_ib_cq_event;
>  
> -	INIT_LIST_HEAD(&cq->wc_list);
>  	kvfree(cqb);
>  	return 0;
>  
> 
> ---
> base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
> change-id: 20261103-free-sw-wcs-8cf40aa66fd8
> 
> Best regards,
> -- 
> Edward Srouji <edwards@nvidia.com>
>