netdev - [PATCH net-next] tcp: socket-specific version of WARN_ON

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Message-Id: <20220729171554.3992869-1-leitao@debian.org>
Date:   Fri, 29 Jul 2022 10:15:54 -0700
From:   Breno Leitao <leitao@...ian.org>
To:     edumazet@...gle.com, davem@...emloft.net, kuba@...nel.org
Cc:     netdev@...r.kernel.org, leit@...com
Subject: [PATCH net-next] tcp: socket-specific version of WARN_ON_ONCE()

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.

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

Signed-off-by: Breno Leitao <leitao@...ian.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 071735e10872..eca7e58a3117 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>
@@ -1216,7 +1217,7 @@ 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 2faaaaf540ac..7abd1634e876 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4556,6 +4556,36 @@ 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