netdev - Re: [PATCH v2] net/mlx5e: Use refcount

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Date:   Sun, 4 Aug 2019 15:58:58 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Chuhong Yuan <hslester96@...il.com>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net/mlx5e: Use refcount_t for refcount

On Sat, Aug 03, 2019 at 12:48:28AM +0800, Chuhong Yuan wrote:
> refcount_t is better for reference counters since its
> implementation can prevent overflows.
> So convert atomic_t ref counters to refcount_t.

I'm not thrilled to see those automatic conversion patches, especially
for flows which can't overflow. There is nothing wrong in using atomic_t
type of variable, do you have in mind flow which will cause to overflow?

Thanks
>
> Signed-off-by: Chuhong Yuan <hslester96@...il.com>
> ---
> Changes in v2:
>   - Add #include.
>
>  drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c
> index b9d4f4e19ff9..148b55c3db7a 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c
> @@ -32,6 +32,7 @@
>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
> +#include <linux/refcount.h>
>  #include <linux/mlx5/driver.h>
>  #include <net/vxlan.h>
>  #include "mlx5_core.h"
> @@ -48,7 +49,7 @@ struct mlx5_vxlan {
>
>  struct mlx5_vxlan_port {
>  	struct hlist_node hlist;
> -	atomic_t refcount;
> +	refcount_t refcount;
>  	u16 udp_port;
>  };
>
> @@ -113,7 +114,7 @@ int mlx5_vxlan_add_port(struct mlx5_vxlan *vxlan, u16 port)
>
>  	vxlanp = mlx5_vxlan_lookup_port(vxlan, port);
>  	if (vxlanp) {
> -		atomic_inc(&vxlanp->refcount);
> +		refcount_inc(&vxlanp->refcount);
>  		return 0;
>  	}
>
> @@ -137,7 +138,7 @@ int mlx5_vxlan_add_port(struct mlx5_vxlan *vxlan, u16 port)
>  	}
>
>  	vxlanp->udp_port = port;
> -	atomic_set(&vxlanp->refcount, 1);
> +	refcount_set(&vxlanp->refcount, 1);
>
>  	spin_lock_bh(&vxlan->lock);
>  	hash_add(vxlan->htable, &vxlanp->hlist, port);
> @@ -170,7 +171,7 @@ int mlx5_vxlan_del_port(struct mlx5_vxlan *vxlan, u16 port)
>  		goto out_unlock;
>  	}
>
> -	if (atomic_dec_and_test(&vxlanp->refcount)) {
> +	if (refcount_dec_and_test(&vxlanp->refcount)) {
>  		hash_del(&vxlanp->hlist);
>  		remove = true;
>  	}
> --
> 2.20.1
>