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

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Date:   Thu, 3 Mar 2022 09:59:28 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Menglong Dong <menglong8.dong@...il.com>
Cc:     David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Menglong Dong <imagedong@...cent.com>,
        Talal Ahmad <talalahmad@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Alexander Lobakin <alobakin@...me>, flyingpeng@...cent.com,
        mengensun@...cent.com, Antoine Tenart <atenart@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Cong Wang <cong.wang@...edance.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next 4/7] net: dev: use kfree_skb_reason() for enqueue_to_backlog()

On Thu, Mar 3, 2022 at 9:48 AM <menglong8.dong@...il.com> wrote:
>
> From: Menglong Dong <imagedong@...cent.com>
>
> 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@...cent.com>
> ---
>  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
>