kernel.git/net/mptcp/protocol.c, branch master

mptcp: allow overridden write_space to be invoked

2026-02-11T03:54:21Z

Future extensions with psock will override their own sk->sk_write_space callback. This patch ensures that the overridden sk_write_space can be invoked by MPTCP. INDIRECT_CALL is used to keep the default path optimised. Note that sk->sk_write_space was never called directly with MPTCP sockets, so changing it to sk_stream_write_space in the init, and using it from mptcp_write_space() is not supposed to change the current behaviour. This patch is shared early to ease discussions around future RFC and avoid confusions with this "fix" that is needed for different future extensions. Suggested-by: Paolo Abeni Co-developed-by: Gang Yan Signed-off-by: Gang Yan Signed-off-by: Geliang Tang Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260206-net-next-mptcp-write_space-override-v2-1-e0b12be818c6@kernel.org Signed-off-by: Jakub Kicinski

mptcp: Change some dubious min_t(int, ...) to min()

2026-02-05T02:45:09Z

There are two: min_t(int, xxx, mptcp_wnd_end(msk) - msk->snd_nxt); Both mptcp_wnd_end(msk) and msk->snd_nxt are u64, their difference (aka the window size) might be limited to 32 bits - but that isn't knowable from this code. So checks being added to min_t() detect the potential discard of significant bits. Provided the 'avail_size' and return of mptcp_check_allowed_size() are changed to an unsigned type (size_t matches the type the caller uses) both min_t() can be changed to min(). Signed-off-by: David Laight Reviewed-by: Matthieu Baerts (NGI0) [ wrapped too long lines when declaring mptcp_check_allowed_size() ] Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-6-31ec8bfc56d1@kernel.org Signed-off-by: Jakub Kicinski

trace: mptcp: add mptcp_rcvbuf_grow tracepoint

2026-02-05T02:45:09Z

Similar to tcp, provide a new tracepoint to better understand mptcp_rcv_space_adjust() behavior, which presents many artifacts. Note that the used format string is so long that I preferred wrap it, contrary to guidance for quoted strings. Reviewed-by: Mat Martineau Signed-off-by: Paolo Abeni Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-4-31ec8bfc56d1@kernel.org Signed-off-by: Jakub Kicinski

mptcp: consolidate rcv space init

2026-02-05T02:45:09Z

MPTCP uses several calls of the mptcp_rcv_space_init() helper to initialize the receive space, with a catch-up call in mptcp_rcv_space_adjust(). Drop all the other strictly not needed invocations and move constant fields initialization at socket init/reset time. This removes a bit of complexity from mptcp DRS code. No functional changes intended. Reviewed-by: Mat Martineau Signed-off-by: Paolo Abeni Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-3-31ec8bfc56d1@kernel.org Signed-off-by: Jakub Kicinski

mptcp: fix receive space timestamp initialization

2026-02-05T02:45:09Z

MPTCP initialize the receive buffer stamp in mptcp_rcv_space_init(), using the provided subflow stamp. Such helper is invoked in several places; for passive sockets, space init happened at clone time. In such scenario, MPTCP ends-up accesses the subflow stamp before its initialization, leading to quite randomic timing for the first receive buffer auto-tune event, as the timestamp for newly created subflow is not refreshed there. Fix the issue moving the stamp initialization out of the mentioned helper, at the data transfer start, and always using a fresh timestamp. Fixes: 013e3179dbd2 ("mptcp: fix rcv space initialization") Reviewed-by: Mat Martineau Signed-off-by: Paolo Abeni Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-2-31ec8bfc56d1@kernel.org Signed-off-by: Jakub Kicinski

mptcp: do not account for OoO in mptcp_rcvbuf_grow()

2026-02-05T02:45:08Z

MPTCP-level OoOs are physiological when multiple subflows are active concurrently and will not cause retransmissions nor are caused by drops. Accounting for them in mptcp_rcvbuf_grow() causes the rcvbuf slowly drifting towards tcp_rmem[2]. Remove such accounting. Note that subflows will still account for TCP-level OoO when the MPTCP-level rcvbuf is propagated. This also closes a subtle and very unlikely race condition with rcvspace init; active sockets with user-space holding the msk-level socket lock, could complete such initialization in the receive callback, after that the first OoO data reaches the rcvbuf and potentially triggering a divide by zero Oops. Fixes: e118cdc34dd1 ("mptcp: rcvbuf auto-tuning improvement") Signed-off-by: Paolo Abeni Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-1-31ec8bfc56d1@kernel.org Signed-off-by: Jakub Kicinski

mptcp: implement .splice_read

2026-02-03T02:15:32Z

This patch implements .splice_read interface of mptcp struct proto_ops as mptcp_splice_read() with reference to tcp_splice_read(). Corresponding to __tcp_splice_read(), __mptcp_splice_read() is defined, invoking mptcp_read_sock() instead of tcp_read_sock(). mptcp_splice_read() is almost the same as tcp_splice_read(), except for sock_rps_record_flow(). Signed-off-by: Geliang Tang Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260130-net-next-mptcp-splice-v2-4-31332ba70d7f@kernel.org Signed-off-by: Jakub Kicinski

mptcp: implement .read_sock

2026-02-03T02:15:31Z

Current in-kernel TCP sockets -- i.e. from nvme_tcp_try_recv() -- need to call .read_sock interface of struct proto_ops, but it's not implemented in MPTCP. This patch implements it with reference to __tcp_read_sock() and __mptcp_recvmsg_mskq(). Corresponding to tcp_recv_skb(), a new helper for MPTCP named mptcp_recv_skb() is added to peek a skb from sk->sk_receive_queue. Compared with __mptcp_recvmsg_mskq(), mptcp_read_sock() uses sk->sk_rcvbuf as the max read length. The LISTEN status is checked before the while loop, and mptcp_recv_skb() and mptcp_cleanup_rbuf() are invoked after the loop. In the loop, all flags checks for __mptcp_recvmsg_mskq() are removed. Reviewed-by: Hannes Reinecke Signed-off-by: Geliang Tang Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260130-net-next-mptcp-splice-v2-2-31332ba70d7f@kernel.org Signed-off-by: Jakub Kicinski

mptcp: add eat_recv_skb helper

2026-02-03T02:15:31Z

This patch extracts the free skb related code in __mptcp_recvmsg_mskq() into a new helper mptcp_eat_recv_skb(). This new helper will be used in the next patch. Signed-off-by: Geliang Tang Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260130-net-next-mptcp-splice-v2-1-31332ba70d7f@kernel.org Signed-off-by: Jakub Kicinski

mptcp: only reset subflow errors when propagated

2026-01-29T04:58:50Z

Some subflow socket errors need to be reported to the MPTCP socket: the initial subflow connect (MP_CAPABLE), and the ones from the fallback sockets. The others are not propagated. The issue is that sock_error() was used to retrieve the error, which was also resetting the sk_err field. Because of that, when notifying the userspace about subflow close events later on from the MPTCP worker, the ssk->sk_err field was always 0. Now, the error (sk_err) is only reset when propagating it to the msk. Fixes: 15cc10453398 ("mptcp: deliver ssk errors to msk") Cc: stable@vger.kernel.org Reviewed-by: Geliang Tang Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260127-net-mptcp-dup-nl-events-v1-3-7f71e1bc4feb@kernel.org Signed-off-by: Jakub Kicinski