The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 2ea6190f42d0416a4310e60a7fcb0b49fcbbd4fb # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025122952-supervise-regulate-a26b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2ea6190f42d0416a4310e60a7fcb0b49fcbbd4fb Mon Sep 17 00:00:00 2001 From: Paolo Abeni pabeni@redhat.com Date: Fri, 5 Dec 2025 19:55:16 +0100 Subject: [PATCH] mptcp: schedule rtx timer only after pushing data

The MPTCP protocol usually schedule the retransmission timer only when there is some chances for such retransmissions to happen.

With a notable exception: __mptcp_push_pending() currently schedule such timer unconditionally, potentially leading to unnecessary rtx timer expiration.

The issue is present since the blamed commit below but become easily reproducible after commit 27b0e701d387 ("mptcp: drop bogus optimization in __mptcp_check_push()")

Fixes: 33d41c9cd74c ("mptcp: more accurate timeout") Cc: stable@vger.kernel.org Signed-off-by: Paolo Abeni pabeni@redhat.com Reviewed-by: Matthieu Baerts (NGI0) matttbe@kernel.org Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org Link: https://patch.msgid.link/20251205-net-mptcp-misc-fixes-6-19-rc1-v1-3-9e4781a... Signed-off-by: Jakub Kicinski kuba@kernel.org

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index e212c1374bd0..d8a7f7029164 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -1623,7 +1623,7 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags) struct mptcp_sendmsg_info info = { .flags = flags, }; - bool do_check_data_fin = false; + bool copied = false; int push_count = 1;

while (mptcp_send_head(sk) && (push_count > 0)) { @@ -1665,7 +1665,7 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags) push_count--; continue; } - do_check_data_fin = true; + copied = true; } } } @@ -1674,11 +1674,14 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags) if (ssk) mptcp_push_release(ssk, &info);

- /* ensure the rtx timer is running */ - if (!mptcp_rtx_timer_pending(sk)) - mptcp_reset_rtx_timer(sk); - if (do_check_data_fin) + /* Avoid scheduling the rtx timer if no data has been pushed; the timer + * will be updated on positive acks by __mptcp_cleanup_una(). + */ + if (copied) { + if (!mptcp_rtx_timer_pending(sk)) + mptcp_reset_rtx_timer(sk); mptcp_check_send_data_fin(sk); + } }

static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk, bool first)