netdev - Re: [PATCH 1/2] bnxt_en: Use refcount

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Date:   Wed, 31 Jul 2019 12:05:22 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Chuhong Yuan <hslester96@...il.com>
Cc:     Michael Chan <michael.chan@...adcom.com>,
        "David S . Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] bnxt_en: Use refcount_t for refcount

On Wed, Jul 31, 2019 at 8:22 AM Chuhong Yuan <hslester96@...il.com> wrote:
>
> refcount_t is better for reference counters since its
> implementation can prevent overflows.
> So convert atomic_t ref counters to refcount_t.
>
> Signed-off-by: Chuhong Yuan <hslester96@...il.com>
> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c | 8 ++++----
>  drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.h | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c
> index fc77caf0a076..eb7ed34639e2 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c
> @@ -49,7 +49,7 @@ static int bnxt_register_dev(struct bnxt_en_dev *edev, int ulp_id,
>                         return -ENOMEM;
>         }
>
> -       atomic_set(&ulp->ref_count, 0);
> +       refcount_set(&ulp->ref_count, 0);

One feature of refcount_t is that it warns on refcount_inc from 0 to
detect possible use-after_free. It appears that that can trigger here?

>         ulp->handle = handle;
>         rcu_assign_pointer(ulp->ulp_ops, ulp_ops);
>
> @@ -246,12 +246,12 @@ static int bnxt_send_msg(struct bnxt_en_dev *edev, int ulp_id,
>
>  static void bnxt_ulp_get(struct bnxt_ulp *ulp)
>  {
> -       atomic_inc(&ulp->ref_count);
> +       refcount_inc(&ulp->ref_count);
>  }