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[86.153.201.25]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f4635c86csm19224122f8f.16.2026.07.15.14.35.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jul 2026 14:35:43 -0700 (PDT) From: Nnamdi Onyeyiri To: jiayuan.chen@linux.dev Cc: bpf@vger.kernel.org, davem@davemloft.net, edumazet@google.com, horms@kernel.org, jakub@cloudflare.com, john.fastabend@gmail.com, kuba@kernel.org, kuniyu@google.com, ncardwell@google.com, netdev@vger.kernel.org, nnamdio@gmail.com, pabeni@redhat.com, sashiko-reviews@lists.linux.dev Subject: [PATCH v4 1/2] bpf, sockmap: handle spurious tcp_msg_wait_data() wakeup Date: Wed, 15 Jul 2026 22:35:37 +0100 Message-ID: <20260715213538.37229-2-nnamdio@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260715213538.37229-1-nnamdio@gmail.com> References: <5b07d2ab-84ee-46ae-84c9-7542499d26d7@linux.dev> <20260715213538.37229-1-nnamdio@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit recvfrom()/recv() are documented as only returning EAGAIN for blocking sockets when they have a receive timeout configured. However, adding a blocking ipv4 tcp socket without a receive timeout to a sockmap will cause EAGAIN errors sporadically. A socket with a receive timeout may return EAGAIN before the timeout expires. There are 2 code paths affected by this: 1. tcp_bpf_recvmsg() - Used when the socket has been added to a sockmap that has no verdict program attached. 2. tcp_bpf_recvmsg_parser() - Used when the socket has been added to a sockmap that has a verdict program. To reproduce this issue, it is enough for the verdict program to do nothing but return SK_PASS. In both cases this happens when tcp_msg_wait_data() wakes spuriously (returning 0). To fix it, we now loop back to msg_bytes_ready instead of returning -EAGAIN on spurious wakeup. To ensure the looping does not cause sockets with a SO_RCVTIMEO set to wait excessively long, tcp_msg_wait_data() now takes a pointer to timeo, allowing sk_wait_event() to update it as appropriate. The logic in tcp_bpf_recvmsg_parser() that allow it to handle signals, socket errors and closuers in its loop was also added to tcp_bpf_recvmsg(). Signed-off-by: Nnamdi Onyeyiri --- net/ipv4/tcp_bpf.c | 69 ++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 60 insertions(+), 9 deletions(-) diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index cc0bd73f36b6..aa5c5d741599 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -179,7 +179,7 @@ EXPORT_SYMBOL_GPL(tcp_bpf_sendmsg_redir); #ifdef CONFIG_BPF_SYSCALL static int tcp_msg_wait_data(struct sock *sk, struct sk_psock *psock, - long timeo) + long *timeo) { DEFINE_WAIT_FUNC(wait, woken_wake_function); int ret = 0; @@ -187,12 +187,12 @@ static int tcp_msg_wait_data(struct sock *sk, struct sk_psock *psock, if (sk->sk_shutdown & RCV_SHUTDOWN) return 1; - if (!timeo) + if (!*timeo) return ret; add_wait_queue(sk_sleep(sk), &wait); sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk); - ret = sk_wait_event(sk, &timeo, + ret = sk_wait_event(sk, timeo, !list_empty(&psock->ingress_msg) || !skb_queue_empty_lockless(&sk->sk_receive_queue), &wait); sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk); @@ -229,6 +229,7 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, int copied_from_self = 0; int copied = 0; u32 seq; + long timeo; if (unlikely(flags & MSG_ERRQUEUE)) return inet_recv_error(sk, msg, len); @@ -262,6 +263,8 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, } } + timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); + msg_bytes_ready: copied = __sk_msg_recvmsg(sk, psock, msg, len, flags, &copied_from_self); /* The typical case for EFAULT is the socket was gracefully @@ -280,7 +283,6 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, } seq += copied_from_self; if (!copied) { - long timeo; int data; if (sock_flag(sk, SOCK_DONE)) @@ -299,7 +301,6 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, goto out; } - timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); if (!timeo) { copied = -EAGAIN; goto out; @@ -310,13 +311,15 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, goto out; } - data = tcp_msg_wait_data(sk, psock, timeo); + data = tcp_msg_wait_data(sk, psock, &timeo); if (data < 0) { copied = data; goto unlock; } if (data && !sk_psock_queue_empty(psock)) goto msg_bytes_ready; + if (!data && timeo > 0) + goto msg_bytes_ready; copied = -EAGAIN; } out: @@ -355,6 +358,7 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, { struct sk_psock *psock; int copied, ret; + long timeo; if (unlikely(flags & MSG_ERRQUEUE)) return inet_recv_error(sk, msg, len); @@ -371,14 +375,59 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, return tcp_recvmsg(sk, msg, len, flags); } lock_sock(sk); + + timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); + msg_bytes_ready: copied = sk_msg_recvmsg(sk, psock, msg, len, flags); if (!copied) { - long timeo; int data; - timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); - data = tcp_msg_wait_data(sk, psock, timeo); + if (sock_flag(sk, SOCK_DONE)) { + ret = 0; + goto unlock; + } + + if (sk->sk_err) { + if (!sk_psock_queue_empty(psock)) + goto msg_bytes_ready; + if (!skb_queue_empty(&sk->sk_receive_queue)) { + release_sock(sk); + sk_psock_put(sk, psock); + return tcp_recvmsg(sk, msg, len, flags); + } + ret = sock_error(sk); + goto unlock; + } + + if (sk->sk_shutdown & RCV_SHUTDOWN) { + if (!sk_psock_queue_empty(psock)) + goto msg_bytes_ready; + if (!skb_queue_empty(&sk->sk_receive_queue)) { + release_sock(sk); + sk_psock_put(sk, psock); + return tcp_recvmsg(sk, msg, len, flags); + } + ret = 0; + goto unlock; + } + + if (sk->sk_state == TCP_CLOSE) { + ret = -ENOTCONN; + goto unlock; + } + + if (!timeo) { + ret = -EAGAIN; + goto unlock; + } + + if (signal_pending(current)) { + ret = sock_intr_errno(timeo); + goto unlock; + } + + data = tcp_msg_wait_data(sk, psock, &timeo); if (data < 0) { ret = data; goto unlock; @@ -390,6 +439,8 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, sk_psock_put(sk, psock); return tcp_recvmsg(sk, msg, len, flags); } + if (!data && timeo > 0) + goto msg_bytes_ready; copied = -EAGAIN; } ret = copied; -- 2.52.0