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[107.190.31.17]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2cf3473ba1dsm62513545ad.65.2026.07.20.14.16.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jul 2026 14:16:09 -0700 (PDT) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 20 Jul 2026 17:16:08 -0400 Message-Id: Cc: , , , , , , , , , , , , , Subject: Re: [PATCH v6 1/2] bpf, sockmap: handle spurious tcp_msg_wait_data() wakeup From: "Emil Tsalapatis" To: "Nnamdi Onyeyiri" X-Mailer: aerc 0.20.1 References: <20260720171535.67867-1-nnamdio@gmail.com> <20260720171535.67867-2-nnamdio@gmail.com> In-Reply-To: <20260720171535.67867-2-nnamdio@gmail.com> On Mon Jul 20, 2026 at 1:15 PM EDT, Nnamdi Onyeyiri wrote: > recvfrom()/recv() are documented as only returning EAGAIN for blocking so= ckets > 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 t= he > 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); > =20 > #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 =3D 0; > @@ -187,12 +187,12 @@ static int tcp_msg_wait_data(struct sock *sk, struc= t sk_psock *psock, > if (sk->sk_shutdown & RCV_SHUTDOWN) > return 1; > =20 > - if (!timeo) > + if (!*timeo) > return ret; > =20 > add_wait_queue(sk_sleep(sk), &wait); > sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk); > - ret =3D sk_wait_event(sk, &timeo, > + ret =3D 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 =3D 0; > int copied =3D 0; > u32 seq; > + long timeo; > =20 > 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, > } > } > =20 > + timeo =3D sock_rcvtimeo(sk, flags & MSG_DONTWAIT); > + > msg_bytes_ready: > copied =3D __sk_msg_recvmsg(sk, psock, msg, len, flags, &copied_from_se= lf); > /* The typical case for EFAULT is the socket was gracefully > @@ -280,7 +283,6 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, > } > seq +=3D copied_from_self; > if (!copied) { > - long timeo; > int data; > =20 > if (sock_flag(sk, SOCK_DONE)) > @@ -299,7 +301,6 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, > goto out; > } > =20 > - timeo =3D sock_rcvtimeo(sk, flags & MSG_DONTWAIT); > if (!timeo) { > copied =3D -EAGAIN; > goto out; > @@ -310,13 +311,15 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, > goto out; > } > =20 > - data =3D tcp_msg_wait_data(sk, psock, timeo); > + data =3D tcp_msg_wait_data(sk, psock, &timeo); > if (data < 0) { > copied =3D data; > goto unlock; > } > if (data && !sk_psock_queue_empty(psock)) > goto msg_bytes_ready; > + if (!data && timeo > 0) > + goto msg_bytes_ready; > copied =3D -EAGAIN; > } > out: > @@ -355,6 +358,7 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct ms= ghdr *msg, size_t len, > { > struct sk_psock *psock; > int copied, ret; > + long timeo; > =20 > 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 =3D sock_rcvtimeo(sk, flags & MSG_DONTWAIT); > + > msg_bytes_ready: > copied =3D sk_msg_recvmsg(sk, psock, msg, len, flags); > if (!copied) { > - long timeo; > int data; > =20 > - timeo =3D sock_rcvtimeo(sk, flags & MSG_DONTWAIT); > - data =3D tcp_msg_wait_data(sk, psock, timeo); > + if (sock_flag(sk, SOCK_DONE)) { > + ret =3D 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 =3D 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 =3D 0; > + goto unlock; These two error handling routines above look identical. Can you refactor them? > + } > + > + if (sk->sk_state =3D=3D TCP_CLOSE) { > + ret =3D -ENOTCONN; > + goto unlock; > + } > + > + if (!timeo) { > + ret =3D -EAGAIN; > + goto unlock; > + } > + Since this handling (which Sashiko flags by the way, correctly AFAICT)=20 are taken from tcp_bpf_recvmsg, there is obvious overlap between the two functions. Please factor those out so that they share the logic between them. pw-bot: cr > + if (signal_pending(current)) { > + ret =3D sock_intr_errno(timeo); > + goto unlock; > + } > + > + data =3D tcp_msg_wait_data(sk, psock, &timeo); > if (data < 0) { > ret =3D data; > goto unlock; > @@ -390,6 +439,8 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct ms= ghdr *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 =3D -EAGAIN; > } > ret =3D copied;