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[86.153.201.25]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-495653c9d99sm101290455e9.12.2026.07.21.15.38.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jul 2026 15:38:12 -0700 (PDT) From: Nnamdi Onyeyiri To: nnamdio@gmail.com Cc: bpf@vger.kernel.org, davem@davemloft.net, edumazet@google.com, horms@kernel.org, jakub@cloudflare.com, jiayuan.chen@linux.dev, john.fastabend@gmail.com, kuba@kernel.org, kuniyu@google.com, ncardwell@google.com, netdev@vger.kernel.org, pabeni@redhat.com, sashiko-reviews@lists.linux.dev, linux-kernel@vger.kernel.org, emil@etsalapatis.com Subject: [PATCH v7 1/2] bpf, sockmap: handle spurious tcp_msg_wait_data() wakeup Date: Tue, 21 Jul 2026 23:38:06 +0100 Message-ID: <20260721223807.75101-2-nnamdio@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260721223807.75101-1-nnamdio@gmail.com> References: <20260721223807.75101-1-nnamdio@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@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" 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 | 72 ++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 63 insertions(+), 9 deletions(-) diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index cc0bd73f36b6..1755fcf726fc 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, struct = 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_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 +=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 msgh= dr *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 +375,52 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct ms= ghdr *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 check_queues; + } + + 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) { + ret =3D 0; + goto check_queues; + } + + if (sk->sk_state =3D=3D TCP_CLOSE) { + ret =3D -ENOTCONN; + goto check_queues; + } + + if (!timeo) { + ret =3D -EAGAIN; + goto check_queues; + } + + if (signal_pending(current)) { + ret =3D sock_intr_errno(timeo); + goto check_queues; + } + + data =3D tcp_msg_wait_data(sk, psock, &timeo); if (data < 0) { ret =3D data; goto unlock; @@ -390,6 +432,8 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msgh= dr *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; @@ -398,6 +442,16 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msg= hdr *msg, size_t len, release_sock(sk); sk_psock_put(sk, psock); 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[86.153.201.25]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-495653c9d99sm101290455e9.12.2026.07.21.15.38.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jul 2026 15:38:12 -0700 (PDT) From: Nnamdi Onyeyiri To: nnamdio@gmail.com Cc: bpf@vger.kernel.org, davem@davemloft.net, edumazet@google.com, horms@kernel.org, jakub@cloudflare.com, jiayuan.chen@linux.dev, john.fastabend@gmail.com, kuba@kernel.org, kuniyu@google.com, ncardwell@google.com, netdev@vger.kernel.org, pabeni@redhat.com, sashiko-reviews@lists.linux.dev, linux-kernel@vger.kernel.org, emil@etsalapatis.com Subject: [PATCH v7 2/2] selftests/bpf: add sockmap recvfrom EAGAIN selftest Date: Tue, 21 Jul 2026 23:38:07 +0100 Message-ID: <20260721223807.75101-3-nnamdio@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260721223807.75101-1-nnamdio@gmail.com> References: <20260721223807.75101-1-nnamdio@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@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" These selftests exercise the tcp_bpf_recvmsg() and tcp_bpf_recvmsg_parser() functions, to ensure that they are properly handling spurious wakeups in tcp_msg_wait_data(). The expected behaviour is that recvfrom() does not return an EAGAIN error. If the spurious wakeups are incorrectly handled, this assertion will fail. Signed-off-by: Nnamdi Onyeyiri --- .../selftests/bpf/prog_tests/sockmap_basic.c | 136 ++++++++++++++++++ 1 file changed, 136 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c b/tools= /testing/selftests/bpf/prog_tests/sockmap_basic.c index cb3229711f93..afda4d90e573 100644 --- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c @@ -1373,6 +1373,138 @@ static void test_sockmap_multi_channels(int sotype) test_sockmap_pass_prog__destroy(skel); } =20 +static void *test_sockmap_recvfrom_eagain_thread(void *arg) +{ + int fd =3D *(int *)arg; + char buf[1024]; + void *result =3D NULL; + + while (true) { + ssize_t len =3D recvfrom(fd, buf, sizeof(buf), 0, NULL, NULL); + + if (len =3D=3D -1) { + if (errno =3D=3D EINTR) + continue; + result =3D (void *)1; + break; + } + + if (!len || buf[len - 1] =3D=3D 'e') + break; + } + + send(fd, "test", 4, MSG_NOSIGNAL); + + close(fd); + + return result; +} + +static void test_sockmap_recvfrom_eagain(bool with_verdict) +{ + struct test_sockmap_pass_prog *skel =3D NULL; + struct bpf_program *prog =3D NULL; + char *buf =3D NULL; + int map, err; + + /* + * the size of the buffer to send. completion of the sending can trigger= a spurious wake + * up. larger values make the issue more likely, but make successful tes= t runs longer. + */ + const size_t buflen =3D 1024 * 1024 * 25; + + /* + * maximum number of attempts to reproduce EAGAIN on spurious wake up. m= ore attempts + * increases the chances of triggering the issue, and the test ends as so= on as we do. + * however, successful runs would take longer to complete. + */ + const int max_attempts =3D 300; + + skel =3D test_sockmap_pass_prog__open_and_load(); + if (!ASSERT_OK_PTR(skel, "open_and_load")) + return; + + map =3D bpf_map__fd(skel->maps.sock_map_rx); + + if (with_verdict) { + prog =3D skel->progs.prog_skb_verdict; + err =3D bpf_prog_attach(bpf_program__fd(prog), map, BPF_SK_SKB_STREAM_VE= RDICT, 0); + if (!ASSERT_OK(err, "bpf_prog_attach verdict")) + goto cleanup; + } + + buf =3D malloc(buflen); + if (!ASSERT_OK_PTR(buf, "malloc buf")) + goto cleanup; + memset(buf, 0, buflen); + buf[buflen - 1] =3D 'e'; + + for (int i =3D 0; i < max_attempts; ++i) { + ssize_t len; + char ignored[128]; + pthread_t thread; + bool thread_created =3D false; + size_t rem =3D buflen; + int c =3D -1, p =3D -1, zero =3D 0; + bool success =3D false; + + err =3D create_pair(AF_INET, SOCK_STREAM, &c, &p); + if (!ASSERT_OK(err, "create_pair")) + goto end_attempt; + + err =3D pthread_create(&thread, NULL, &test_sockmap_recvfrom_eagain_thre= ad, &p); + if (!ASSERT_OK(err, "pthread_create")) + goto end_attempt; + thread_created =3D true; + + err =3D bpf_map_update_elem(map, &zero, &c, BPF_ANY); + if (!ASSERT_OK(err, "bpf_map_update_elem")) + goto end_attempt; + + while (rem) { + len =3D xsend(c, buf + (buflen - rem), rem, 0); + if (len =3D=3D -1) + goto end_attempt; + rem -=3D len; + } + + /* we cannot use recv_timeout(), otherwise EAGAIN would be an expected e= rrno. */ + len =3D recvfrom(c, ignored, sizeof(ignored), 0, NULL, NULL); + + /* + * we are checking for the invalid return of EAGAIN, any other return is= considered + * successful for the purposes of this test. + */ + if (len < 0 && !ASSERT_NEQ(errno, EAGAIN, "recvfrom eagain")) + goto end_attempt; + + success =3D true; + +end_attempt: + if (c >=3D 0) + close(c); + + if (thread_created) { + void *retval =3D NULL; + + pthread_join(thread, &retval); + if (!ASSERT_NULL(retval, "retval")) + success =3D false; + } + + if (!thread_created && p >=3D 0) + close(p); + if (!success) + break; + } + +cleanup: + if (buf) + free(buf); + + test_sockmap_pass_prog__destroy(skel); +} + void test_sockmap_basic(void) { if (test__start_subtest("sockmap create_update_free")) @@ -1451,4 +1583,8 @@ void test_sockmap_basic(void) test_sockmap_multi_channels(SOCK_STREAM); if (test__start_subtest("sockmap udp multi channels")) test_sockmap_multi_channels(SOCK_DGRAM); + if (test__start_subtest("sockmap recvfrom eagain")) + test_sockmap_recvfrom_eagain(false); + if (test__start_subtest("sockmap recvfrom eagain with verdict")) + test_sockmap_recvfrom_eagain(true); } --=20 2.52.0