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

[Menglong Dong]

On Fri, Mar 4, 2022 at 1:59 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> 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;
>

Yeah, this 'else' can be omitted :) Thanks!

>
> > +               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
> >