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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4909c09ab75sm18738075e9.6.2026.05.29.10.45.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 May 2026 10:45:31 -0700 (PDT) From: David Carlier To: mptcp@lists.linux.dev Cc: matttbe@kernel.org, martineau@kernel.org, geliang@kernel.org, pabeni@redhat.com, David Carlier Subject: [PATCH mptcp-next v10 3/4] mptcp: support MSG_ERRQUEUE on the parent socket Date: Fri, 29 May 2026 18:45:21 +0100 Message-ID: <20260529174524.260199-4-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260529174524.260199-1-devnexen@gmail.com> References: <20260529174524.260199-1-devnexen@gmail.com> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Splice pending err skbs from each subflow's error queue onto the parent msk's error queue at error-report time, so poll() and recvmsg(MSG_ERRQUEUE) on the parent socket observe TX timestamps and MSG_ZEROCOPY completion notifications through the standard inet ABI. The splice filters by SO_EE_ORIGIN: TIMESTAMPING / ZEROCOPY / LOCAL events forward to the parent because they are tied to user-handed data, not to a specific path; subflow-level ICMP errors are dropped because the legacy RECVERR ABI cannot meaningfully convey their per-subflow peer identity to single-path-aware userspace. Such events will be carried by a future MPTCP_RECERR channel. MSG_ZEROCOPY completions carry an unpin/free obligation for userspace, so they are queued to the parent unconditionally and are never dropped, mirroring tcp's __msg_zerocopy_callback() which likewise bypasses sk_rcvbuf. Timestamping and local events instead go through sock_queue_err_skb() and are dropped under rmem pressure (sk_rmem_alloc + truesize >= sk_rcvbuf) on a full err queue, matching tcp's sk_rcvbuf-gated tx-timestamp path and ip_icmp_error() / ipv6_icmp_error(). The MSG_ERRQUEUE branch of mptcp_recvmsg() forwards to inet_recv_error() directly, and poll() advertises EPOLLERR purely on the parent's sk_err / sk_error_queue, matching tcp_poll(). Suggested-by: Paolo Abeni Signed-off-by: David Carlier --- net/mptcp/protocol.c | 68 ++++++++++++++++++++++++++++++++++++++------ 1 file changed, 59 insertions(+), 9 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 1d67728d4233..64c0e841b9b7 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -11,6 +11,7 @@ #include #include #include +#include #include #include #include @@ -829,21 +830,66 @@ static bool __mptcp_ofo_queue(struct mptcp_sock *msk) return moved; } +static bool mptcp_errqueue_skb_forwardable(const struct sk_buff *skb) +{ + u8 origin = SKB_EXT_ERR(skb)->ee.ee_origin; + + return origin == SO_EE_ORIGIN_TIMESTAMPING || + origin == SO_EE_ORIGIN_ZEROCOPY || + origin == SO_EE_ORIGIN_LOCAL; +} + +static bool __mptcp_subflow_splice_errqueue(struct sock *sk, struct sock *ssk) +{ + struct sk_buff *skb; + bool moved = false; + + while ((skb = skb_dequeue(&ssk->sk_error_queue))) { + if (!mptcp_errqueue_skb_forwardable(skb)) { + kfree_skb(skb); /* path-specific (ICMP) — belongs in MPTCP_RECERR */ + continue; + } + /* MSG_ZEROCOPY completions carry an unpin/free obligation for + * userspace and must never be dropped. TCP's + * __msg_zerocopy_callback() queues them to sk_error_queue + * regardless of sk_rcvbuf; mirror that here rather than letting + * sock_queue_err_skb() drop them under receive-buffer pressure. + */ + if (SKB_EXT_ERR(skb)->ee.ee_origin == SO_EE_ORIGIN_ZEROCOPY) { + skb_orphan(skb); + skb->sk = sk; + skb_queue_tail(&sk->sk_error_queue, skb); + moved = true; + continue; + } + if (sock_queue_err_skb(sk, skb)) { + kfree_skb(skb); + continue; + } + moved = true; + } + + return moved; +} + static bool __mptcp_subflow_error_report(struct sock *sk, struct sock *ssk) { + bool propagated = false; int ssk_state; + bool report; int err; + report = __mptcp_subflow_splice_errqueue(sk, ssk); + /* only propagate errors on fallen-back sockets or * on MPC connect */ if (sk->sk_state != TCP_SYN_SENT && !__mptcp_check_fallback(mptcp_sk(sk))) - return false; + goto out; err = sock_error(ssk); if (!err) - return false; - + goto out; /* We need to propagate only transition to CLOSE state. * Orphaned socket will see such state change via * subflow_sched_work_if_closed() and that path will properly @@ -853,11 +899,15 @@ static bool __mptcp_subflow_error_report(struct sock *sk, struct sock *ssk) if (ssk_state == TCP_CLOSE && !sock_flag(sk, SOCK_DEAD)) mptcp_set_state(sk, ssk_state); WRITE_ONCE(sk->sk_err, -err); + report = propagated = true; - /* This barrier is coupled with smp_rmb() in mptcp_poll() */ - smp_wmb(); - sk_error_report(sk); - return true; +out: + if (report) { + /* This barrier is coupled with smp_rmb() in mptcp_poll() */ + smp_wmb(); + sk_error_report(sk); + } + return propagated; } void __mptcp_error_report(struct sock *sk) @@ -2313,7 +2363,6 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int target; long timeo; - /* MSG_ERRQUEUE is really a no-op till we support IP_RECVERR */ if (unlikely(flags & MSG_ERRQUEUE)) return inet_recv_error(sk, msg, len); @@ -4363,7 +4412,8 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock, /* This barrier is coupled with smp_wmb() in __mptcp_error_report() */ smp_rmb(); - if (READ_ONCE(sk->sk_err)) + if (READ_ONCE(sk->sk_err) || + !skb_queue_empty_lockless(&sk->sk_error_queue)) mask |= EPOLLERR; return mask; -- 2.53.0