Re: [PATCH net-next 4/7] net: dev: use kfree_skb_reason() for enqueue_to_backlog()

[Eric Dumazet]

On Thu, Mar 3, 2022 at 9:48 AM <menglong8.dong@xxxxxxxxx> wrote:
>
> From: Menglong Dong <imagedong@xxxxxxxxxxx>
>
> Replace kfree_skb() used in enqueue_to_backlog() with
> kfree_skb_reason(). The skb rop reason SKB_DROP_REASON_CPU_BACKLOG is
> introduced for the case of failing to enqueue the skb to the per CPU
> backlog queue. The further reason can be backlog queue full or RPS
> flow limition, and I think we meedn't to make further distinctions.
>
> Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
> ---
>  include/linux/skbuff.h     | 6 ++++++
>  include/trace/events/skb.h | 1 +
>  net/core/dev.c             | 6 +++++-
>  3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 62f9d15ec6ec..d2cf87ff84c2 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -402,6 +402,12 @@ enum skb_drop_reason {
>                                          * outputting (failed to enqueue to
>                                          * current qdisc)
>                                          */
> +       SKB_DROP_REASON_CPU_BACKLOG,    /* failed to enqueue the skb to
> +                                        * the per CPU backlog queue. This
> +                                        * can be caused by backlog queue
> +                                        * full (see netdev_max_backlog in
> +                                        * net.rst) or RPS flow limit
> +                                        */
>         SKB_DROP_REASON_MAX,
>  };
>
> diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
> index 80fe15d175e3..29c360b5e114 100644
> --- a/include/trace/events/skb.h
> +++ b/include/trace/events/skb.h
> @@ -47,6 +47,7 @@
>         EM(SKB_DROP_REASON_NEIGH_DEAD, NEIGH_DEAD)              \
>         EM(SKB_DROP_REASON_QDISC_EGRESS, QDISC_EGRESS)          \
>         EM(SKB_DROP_REASON_QDISC_DROP, QDISC_DROP)              \
> +       EM(SKB_DROP_REASON_CPU_BACKLOG, CPU_BACKLOG)            \
>         EMe(SKB_DROP_REASON_MAX, MAX)
>
>  #undef EM
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 3280ba2502cd..373fa7a33ffa 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4541,10 +4541,12 @@ static bool skb_flow_limit(struct sk_buff *skb, unsigned int qlen)
>  static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
>                               unsigned int *qtail)
>  {
> +       enum skb_drop_reason reason;
>         struct softnet_data *sd;
>         unsigned long flags;
>         unsigned int qlen;
>
> +       reason = SKB_DROP_REASON_NOT_SPECIFIED;
>         sd = &per_cpu(softnet_data, cpu);
>
>         rps_lock_irqsave(sd, &flags);
> @@ -4566,6 +4568,8 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
>                 if (!__test_and_set_bit(NAPI_STATE_SCHED, &sd->backlog.state))
>                         napi_schedule_rps(sd);
>                 goto enqueue;
> +       } else {

No need for an else {} after a goto  xxx;


> +               reason = SKB_DROP_REASON_CPU_BACKLOG;
>         }
>
>  drop:
> @@ -4573,7 +4577,7 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
>         rps_unlock_irq_restore(sd, &flags);
>
>         atomic_long_inc(&skb->dev->rx_dropped);
> -       kfree_skb(skb);
> +       kfree_skb_reason(skb, reason);
>         return NET_RX_DROP;
>  }
>
> --
> 2.35.1
>