On Tue, Feb 12, 2019 at 11:07 PM Eric Dumazet <eric.duma...@gmail.com> wrote:
>
>
>
> On 02/12/2019 03:31 AM, Yafang Shao wrote:
> > SOCK_DEBUG is a very ancient debugging interface, and it's not very useful
> > for debugging.
> > So this patch removes the SOCK_DEBUG() and introduce a new function
> > tcp_stats() to trace this kind of events.
> > Some MIBs are added for these events.
> >
> > Regarding the SO_DEBUG in sock_{s,g}etsockopt, I think it is better to
> > keep as-is, because if we return an errno to tell the application that
> > this optname isn't supported for TCP, it may break the application.
> > The application still can use this option but don't take any effect for
> > TCP.
> >
> > Signed-off-by: Yafang Shao <laoar.s...@gmail.com>
> > ---
> > include/uapi/linux/snmp.h | 3 +++
> > net/ipv4/proc.c | 3 +++
> > net/ipv4/tcp_input.c | 26 +++++++++++---------------
> > net/ipv6/tcp_ipv6.c | 2 --
> > 4 files changed, 17 insertions(+), 17 deletions(-)
> >
> > diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
> > index 86dc24a..fd5c09c 100644
> > --- a/include/uapi/linux/snmp.h
> > +++ b/include/uapi/linux/snmp.h
> > @@ -283,6 +283,9 @@ enum
> > LINUX_MIB_TCPACKCOMPRESSED, /* TCPAckCompressed */
> > LINUX_MIB_TCPZEROWINDOWDROP, /* TCPZeroWindowDrop */
> > LINUX_MIB_TCPRCVQDROP, /* TCPRcvQDrop */
> > + LINUX_MIB_TCPINVALIDACK, /* TCPInvalidAck */
> > + LINUX_MIB_TCPOLDACK, /* TCPOldAck */
> > + LINUX_MIB_TCPPARTIALPACKET, /* TCPPartialPacket */
> > __LINUX_MIB_MAX
> > };
> >
> > diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
> > index c3610b3..1b0320a 100644
> > --- a/net/ipv4/proc.c
> > +++ b/net/ipv4/proc.c
> > @@ -291,6 +291,9 @@ static int sockstat_seq_show(struct seq_file *seq, void
> > *v)
> > SNMP_MIB_ITEM("TCPAckCompressed", LINUX_MIB_TCPACKCOMPRESSED),
> > SNMP_MIB_ITEM("TCPZeroWindowDrop", LINUX_MIB_TCPZEROWINDOWDROP),
> > SNMP_MIB_ITEM("TCPRcvQDrop", LINUX_MIB_TCPRCVQDROP),
> > + SNMP_MIB_ITEM("TCPInvalidAck", LINUX_MIB_TCPINVALIDACK),
> > + SNMP_MIB_ITEM("TCPOldAck", LINUX_MIB_TCPOLDACK),
> > + SNMP_MIB_ITEM("TCPPartialPacket", LINUX_MIB_TCPPARTIALPACKET),
> > SNMP_MIB_SENTINEL
> > };
> >
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index 7a027dec..88deb1f 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -3554,6 +3554,11 @@ static u32 tcp_newly_delivered(struct sock *sk, u32
> > prior_delivered, int flag)
> > return delivered;
> > }
> >
> > +static void tcp_stats(struct sock *sk, int mib_idx)
> > +{
> > + NET_INC_STATS(sock_net(sk), mib_idx);
> > +}
>
> This is not a very descriptive name.
>
> Why is it static, and in net/ipv4/tcp_input.c ???
>
Because it is only called in net/ipv4/tcp_input.c currently, so I
define it as static in this file,
the reseaon I don't define it as 'static inline' is that I think the
compiler can make a better decision than me.
In the future it may be called in other files, then we can put it into
a more proper file.
> > +
> > /* This routine deals with incoming acks, but not outgoing ones. */
> > static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> > {
> > @@ -3715,7 +3720,7 @@ static int tcp_ack(struct sock *sk, const struct
> > sk_buff *skb, int flag)
> > return 1;
> >
> > invalid_ack:
> > - SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
> > + tcp_stats(sk, LINUX_MIB_TCPINVALIDACK);
> > return -1;
> >
> > old_ack:
> > @@ -3731,7 +3736,7 @@ static int tcp_ack(struct sock *sk, const struct
> > sk_buff *skb, int flag)
> > tcp_xmit_recovery(sk, rexmit);
> > }
> >
> > - SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una,
> > tp->snd_nxt);
> > + tcp_stats(sk, LINUX_MIB_TCPOLDACK);
> > return 0;
> > }
> >
>
>
> These counters will add noise to an already crowded MIB space.
>
I have another idea that we can define some tcp bpf events to replace
these MIB counters somehing like,
#define BPF_EVENT_TCP_OLDACK 1
#define BPF_EVENT_TCP_PARTIALPACKET 2
...
Maybe we could also cleanup some MIBs to make it less crowded.
> What bug do you expect to track and fix with these ?
>
Let me explain the background for you.
I want to track some TCP abnormal behavior in TCP/IP stack. But I
find there's no good way to do it.
The current MIBs are per net, other than per socket, that makes it not
very powerful.
And the ancient SOCK_DEBUG is not good as well.
So we think why not cleanup this ancient SOCK_DEBUG() and introduce a
more powerful method.
> I see many TCP patches coming adding icache pressure, enabling companies to
> build their own modified
> TCP stack, but no real meat.
>
Thanks
Yafang
