Hello~
On Mon, Oct 26, 2020 at 5:52 PM Paolo Abeni <pab...@redhat.com> wrote:
>
> Hello,
>
> On Mon, 2020-10-26 at 17:39 +0800, Menglong Dong wrote:
> > The error returned from __udp_enqueue_schedule_skb is ENOMEM or ENOBUFS.
> > For now, only ENOMEM is counted into UDP_MIB_RCVBUFERRORS in
> > __udp_queue_rcv_skb. UDP_MIB_RCVBUFERRORS should count all of the
> > failed skb because of memory errors during udp receiving, not just because
> > of the limit of sock receive queue. We can see this
> > in __udp4_lib_mcast_deliver:
> >
> > nskb = skb_clone(skb, GFP_ATOMIC);
> >
> > if (unlikely(!nskb)) {
> > atomic_inc(&sk->sk_drops);
> > __UDP_INC_STATS(net, UDP_MIB_RCVBUFERRORS,
> > IS_UDPLITE(sk));
> > __UDP_INC_STATS(net, UDP_MIB_INERRORS,
> > IS_UDPLITE(sk));
> > continue;
> > }
> >
> > See, UDP_MIB_RCVBUFERRORS is increased when skb clone failed. From this
> > point, ENOBUFS from __udp_enqueue_schedule_skb should be counted, too.
> > It means that the buffer used by all of the UDP sock is to the limit, and
> > it ought to be counted.
> >
> > Signed-off-by: Menglong Dong <menglong8.d...@gmail.com>
> > ---
> > net/ipv4/udp.c | 4 +---
> > net/ipv6/udp.c | 4 +---
> > 2 files changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 09f0a23d1a01..49a69d8d55b3 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -2035,9 +2035,7 @@ static int __udp_queue_rcv_skb(struct sock *sk,
> > struct sk_buff *skb)
> > int is_udplite = IS_UDPLITE(sk);
> >
> > /* Note that an ENOMEM error is charged twice */
> > - if (rc == -ENOMEM)
> > - UDP_INC_STATS(sock_net(sk), UDP_MIB_RCVBUFERRORS,
> > - is_udplite);
> > + UDP_INC_STATS(sock_net(sk), UDP_MIB_RCVBUFERRORS, is_udplite);
> > UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
> > kfree_skb(skb);
> > trace_udp_fail_queue_rcv_skb(rc, sk);
> > diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> > index 29d9691359b9..d5e23b150fd9 100644
> > --- a/net/ipv6/udp.c
> > +++ b/net/ipv6/udp.c
> > @@ -634,9 +634,7 @@ static int __udpv6_queue_rcv_skb(struct sock *sk,
> > struct sk_buff *skb)
> > int is_udplite = IS_UDPLITE(sk);
> >
> > /* Note that an ENOMEM error is charged twice */
> > - if (rc == -ENOMEM)
> > - UDP6_INC_STATS(sock_net(sk),
> > - UDP_MIB_RCVBUFERRORS, is_udplite);
> > + UDP6_INC_STATS(sock_net(sk), UDP_MIB_RCVBUFERRORS,
> > is_udplite);
> > UDP6_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
> > kfree_skb(skb);
> > return -1;
>
> The diffstat is nice, but I'm unsure we can do this kind of change
> (well, I really think we should not do it): it will fool any kind of
> existing users (application, scripts, admin) currently reading the
> above counters and expecting UDP_MIB_RCVBUFERRORS being increased with
> the existing schema.
>
> Cheers,
>
> Paolo
>
Well, your words make sense, this change isn't friendly for the existing users.
It really puzzled me when this ENOBUFS happened, no counters were done and
I hardly figured out what happened.
So, is it a good idea to introduce a 'UDP_MIB_MEMERRORS'?
Cheers,
Menglong Dong
