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References: <20220831133758.3741187-1-leitao@debian.org>
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From:   Eric Dumazet <edumazet@google.com>
Date:   Sat, 3 Sep 2022 09:42:43 -0700
Message-ID: <CANn89iLe9spogp7eaXPziA0L-FqJ0w=6VxdWDL6NKGobTyuQRw@mail.gmail.com>
Subject: Re: [PATCH RESEND net-next] tcp: socket-specific version of WARN_ON_ONCE()
To:     Breno Leitao <leitao@debian.org>
Cc:     David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        netdev <netdev@vger.kernel.org>, leit@fb.com,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Paolo Abeni <pabeni@redhat.com>,
        David Ahern <dsahern@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Aug 31, 2022 at 6:38 AM Breno Leitao <leitao@debian.org> wrote:
>
> There are cases where we need information about the socket during a
> warning, so, it could help us to find bugs that happens that do not have
> a easily repro.
>
> BPF congestion control algorithms can change socket state in unexpected
> ways, leading to WARNings. Additional information about the socket state
> is useful to identify the culprit.

Well, this suggests we need to fix BPF side ?

Not sure how this can happen, because TCP_BPF_IW has

if (val <= 0 || tp->data_segs_out > tp->syn_data)
     ret = -EINVAL;
else
    tcp_snd_cwnd_set(tp, val);

It seems you already found the issue in an eBPF CC, can you share the details ?


>
> This diff creates a TCP socket-specific version of WARN_ON_ONCE(), and
> attaches it to tcp_snd_cwnd_set().

Well, I feel this will need constant additions... the state of a
custom BPF CC is opaque to core TCP stack anyway ?

>
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  include/net/tcp.h       |  3 ++-
>  include/net/tcp_debug.h | 10 ++++++++++
>  net/ipv4/tcp.c          | 30 ++++++++++++++++++++++++++++++
>  3 files changed, 42 insertions(+), 1 deletion(-)
>  create mode 100644 include/net/tcp_debug.h
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index d10962b9f0d0..73c3970d8839 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -40,6 +40,7 @@
>  #include <net/inet_ecn.h>
>  #include <net/dst.h>
>  #include <net/mptcp.h>
> +#include <net/tcp_debug.h>
>
>  #include <linux/seq_file.h>
>  #include <linux/memcontrol.h>
> @@ -1222,7 +1223,7 @@ static inline u32 tcp_snd_cwnd(const struct tcp_sock *tp)
>
>  static inline void tcp_snd_cwnd_set(struct tcp_sock *tp, u32 val)
>  {
> -       WARN_ON_ONCE((int)val <= 0);
> +       TCP_SOCK_WARN_ON_ONCE(tp, (int)val <= 0);
>         tp->snd_cwnd = val;
>  }
>
> diff --git a/include/net/tcp_debug.h b/include/net/tcp_debug.h
> new file mode 100644
> index 000000000000..50e96d87d335
> --- /dev/null
> +++ b/include/net/tcp_debug.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_TCP_DEBUG_H
> +#define _LINUX_TCP_DEBUG_H
> +
> +void tcp_sock_warn(const struct tcp_sock *tp);
> +
> +#define TCP_SOCK_WARN_ON_ONCE(tcp_sock, condition) \
> +               DO_ONCE_LITE_IF(condition, tcp_sock_warn, tcp_sock)
> +
> +#endif  /* _LINUX_TCP_DEBUG_H */
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index bbe218753662..71771fee72f7 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -4684,6 +4684,36 @@ int tcp_abort(struct sock *sk, int err)
>  }
>  EXPORT_SYMBOL_GPL(tcp_abort);
>
> +void tcp_sock_warn(const struct tcp_sock *tp)
> +{
> +       const struct sock *sk = (const struct sock *)tp;
> +       struct inet_sock *inet = inet_sk(sk);
> +       struct inet_connection_sock *icsk = inet_csk(sk);
> +
> +       WARN_ON(1);
> +
> +       if (!tp)
> +               return;
> +
> +       pr_warn("Socket Info: family=%u state=%d sport=%u dport=%u ccname=%s cwnd=%u",
> +               sk->sk_family, sk->sk_state, ntohs(inet->inet_sport),
> +               ntohs(inet->inet_dport), icsk->icsk_ca_ops->name, tcp_snd_cwnd(tp));
> +
> +       switch (sk->sk_family) {
> +       case AF_INET:
> +               pr_warn("saddr=%pI4 daddr=%pI4", &inet->inet_saddr,
> +                       &inet->inet_daddr);
> +               break;
> +#if IS_ENABLED(CONFIG_IPV6)
> +       case AF_INET6:
> +               pr_warn("saddr=%pI6 daddr=%pI6", &sk->sk_v6_rcv_saddr,
> +                       &sk->sk_v6_daddr);
> +               break;
> +#endif
> +       }
> +}
> +EXPORT_SYMBOL_GPL(tcp_sock_warn);
> +
>  extern struct tcp_congestion_ops tcp_reno;
>
>  static __initdata unsigned long thash_entries;
> --
> 2.30.2
>