From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f50.google.com (mail-wr1-f50.google.com [209.85.221.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B0218473C61 for ; Wed, 22 Jul 2026 11:22:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784719379; cv=none; b=Kb4JszUEwHRXaxHTJp2uVc097qdG9MHVa5MYRM+OSllbrNh2FHjJ93FHbd4uY6Qio2T1k+/dTPb33j8F4vosLt5Ky0lKfZL1iALYVOP07QWM+5UqlPqw2CM/aJTRD7fpUSUpXIUvZw91QbBrmdXJcyLhTkRwBqhQonIG270GSMM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784719379; c=relaxed/simple; bh=wraTTlefdkdHPNlnRf6WJaDafAqE/c8Ugv2o/ebCXDI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QJtIyncKHjP2B8X4ruEFS1RTqZoPFckkUr76ix98rMIkp+bKZmJc1ONwqI4w29By99shJ8y7uDoGMPzqzqFRpYT+doebhP0HtoMgrI0Zc3/soHQGsQ3YLtWha1azCXSnoZxA+JYTLTzclLW4MEHCHlIdDAOCwk6JEikXCrK9Tzo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=RqHpui6S; arc=none smtp.client-ip=209.85.221.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RqHpui6S" Received: by mail-wr1-f50.google.com with SMTP id ffacd0b85a97d-47f7027ca11so2707663f8f.3 for ; Wed, 22 Jul 2026 04:22:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1784719375; x=1785324175; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=O8RdAVocnPl+oK0nJeH+3MqB3h/AEEqzf4DD+36yYw4=; b=RqHpui6SFLpH3wpo/v8QKyh12bgVBrQwg3fYgq0zAmALR3LXqQKw/ySybgeTeC7U1s 0UO66s3YsyH8yaMEc+GK/Ljz+/ytHqb/+PcSp3ue5px1TNu4Pp0qSzpyjEp45uX64z2t Tl74b8Ah9Yn+LriGI2nc4pDWeA6b6nurd0RquMFxdvkDA+/hJLJAhjeYZfKKsn2z4GBI O4z5g+yy8Bowc5ef8koThP98ZKE/FS9CyVquevzPXilbP0O62C9WtX7I1rzbfenAsA9L dWeOEz8lxP2odOm2Aps9F8+ZjDUBqfcQ9K/YABmOo3dH626EQ5HY0rDwN8iXRFbEnzVi /ERg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784719375; x=1785324175; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=O8RdAVocnPl+oK0nJeH+3MqB3h/AEEqzf4DD+36yYw4=; b=QrrENBlLsR+Lhlwk/TNnRyW2I0GMm36jWbaPHosNHdsiJoktjpAt5tBKFGMOdCR3o8 0JWTVsbZLqbGAprgdumR+uADjAHRv/8TlHLd7tA7BYhSyU0q7S8OSRndyahsu7ZRBOXb U55UzQUBSj1pbNVe66h+i5P1VudqIRsWEM8qMmMEiXvPWRegwvpeR5/+0FX8XzAj71Cs 08CDDxn8IZgJdm7/r6XIibgk8tfbjX0xMblny6c5ejM+5qlqTioVofoZyaZKOsFk0TgB rIxd+gMbp1ItxtUQ5Oeezllz3nlkeR5aBCDGkeW8VUIYz/bqsosg5TA50e7kSyJ31iMx v1pg== X-Forwarded-Encrypted: i=1; AHgh+RqhKiMW/B8CXd5+NIxrQm3+x/15LOrMDIDvBcPBqYumbjX6KlEdVFYWcSvAZtMQ20apiNSiqRG9SQ2FRwE=@vger.kernel.org X-Gm-Message-State: AOJu0Yx4OShDTMU5WTep+d1YC0Y6CvPnKFR+MQC4C5iK/5wGE7p5MUGC N45X/fu/pN//zcRHIhMuzWo6S+0aW6Y/8EvgsRutMoZuAIPTRWIvDQhR X-Gm-Gg: AR+sD11O70tgu8zRkDOqOloNVU8V80b/S5g4vCWBiwCr2XTv9bFFiMTlUyyWekFmM2/ uzvDrmJeq50m08yI3q4E5wKF+CS7yjpfO+5asrWAJd5MfXWTxFn5B5s1dDjwri2D41IzOK2I4I1 HZYzkXq1X5mgVDo04uSrneYKS+XFB+bfuTwrm5KuANo+nUr6cjf72Mvw1pqO760UniiTl1n+9he 0TCPbpNgq++iNzlvp8t6qbwW27oK6Enzhrn+CwLBIHSZNLB7YnUSZc+Ua7AA8AePYk9ORDRzUvB kGalPvfJYzVyvz9gjdMA0cZFRFKA9F56cEbDpCIFYHMzC1DMjN8ZRJMD6nM36LdQd2cjctyy/Ce weozt0s3hK4L635817fCszoPg7Yt6/exHXrIb15P3kiICmwi+PfsB/GZqgl4OEy6Dfnh7P656Wh GXVWPPyQUNK9Xhmo7ADsi9c9eR7wy7pmtt/SbfJ65IOGRGmEeP3xE1wDMkysaXQUPD9g== X-Received: by 2002:a05:6000:400f:b0:47f:8152:e568 with SMTP id ffacd0b85a97d-47f8152e595mr7876397f8f.60.1784719374568; Wed, 22 Jul 2026 04:22:54 -0700 (PDT) Received: from localhost.localdomain (host86-153-201-25.range86-153.btcentralplus.com. [86.153.201.25]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f85c531afsm4884918f8f.24.2026.07.22.04.22.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 04:22:53 -0700 (PDT) Date: Wed, 22 Jul 2026 12:22:52 +0100 From: Nnamdi Onyeyiri To: Jakub Sitnicki Cc: bpf@vger.kernel.org, davem@davemloft.net, edumazet@google.com, horms@kernel.org, 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: Re: [PATCH v7 1/2] bpf, sockmap: handle spurious tcp_msg_wait_data() wakeup Message-ID: References: <20260721223807.75101-1-nnamdio@gmail.com> <20260721223807.75101-2-nnamdio@gmail.com> <87tsprl24q.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87tsprl24q.fsf@cloudflare.com> On Wed, Jul 22, 2026 at 01:01:09PM +0200, Jakub Sitnicki wrote: > On Tue, Jul 21, 2026 at 11:38 PM +01, Nnamdi Onyeyiri wrote: > > 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); > > > > #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 +375,52 @@ 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 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 = sock_error(sk); > > + goto unlock; > > + } > > Isn't that branch the same as: > > if (sk->sk_err) { > ret = sock_error(sk); > goto check_queues; > } > > ? > sock_error clears the error in sk->sk_err. using check_queues means tcp_recvmsg would not see it. is that ok? > > + > > + if (sk->sk_shutdown & RCV_SHUTDOWN) { > > + ret = 0; > > + goto check_queues; > > + } > > + > > + if (sk->sk_state == TCP_CLOSE) { > > + ret = -ENOTCONN; > > + goto check_queues; > > + } > > + > > + if (!timeo) { > > + ret = -EAGAIN; > > + goto check_queues; > > + } > > + > > + if (signal_pending(current)) { > > + ret = sock_intr_errno(timeo); > > + goto check_queues; > > + } > > + > > + data = tcp_msg_wait_data(sk, psock, &timeo); > > if (data < 0) { > > ret = data; > > goto unlock; > > @@ -390,6 +432,8 @@ 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; > > @@ -398,6 +442,16 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, > > release_sock(sk); > > sk_psock_put(sk, psock); > > return ret; > > + > > +check_queues: > > + 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); > > + } > > + goto unlock; > > } > > > > static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock,