Hi Greg, Sasha,

On 03/11/2025 02:38, gregkh@linuxfoundation.org wrote:

This is a note to let you know that I've just added the patch titled

mptcp: drop bogus optimization in __mptcp_check_push()

to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: mptcp-drop-bogus-optimization-in-__mptcp_check_push.patch and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

Can you please drop this patch from v5.15? It looks like it is causing some issues with MP_PRIO tests. I think that's because back then, the path is selected differently, with the use of 'msk->last_snd' which will bypass some decisions to where to send the next data.

I will try to check if another version of this patch is needed for v5.15.

Cheers, Matt

(I kept the patch below just in case some people from the MPTCP ML want to react.)

From stable+bounces-192087-greg=kroah.com@vger.kernel.org Mon Nov 3 05:15:58 2025 From: Sasha Levin sashal@kernel.org Date: Sun, 2 Nov 2025 15:15:50 -0500 Subject: mptcp: drop bogus optimization in __mptcp_check_push() To: stable@vger.kernel.org Cc: Paolo Abeni pabeni@redhat.com, Geliang Tang geliang@kernel.org, Mat Martineau martineau@kernel.org, "Matthieu Baerts (NGI0)" matttbe@kernel.org, Jakub Kicinski kuba@kernel.org, Sasha Levin sashal@kernel.org Message-ID: 20251102201550.3588174-1-sashal@kernel.org

From: Paolo Abeni pabeni@redhat.com

[ Upstream commit 27b0e701d3872ba59c5b579a9e8a02ea49ad3d3b ]

Accessing the transmit queue without owning the msk socket lock is inherently racy, hence __mptcp_check_push() could actually quit early even when there is pending data.

That in turn could cause unexpected tx lock and timeout.

Dropping the early check avoids the race, implicitly relaying on later tests under the relevant lock. With such change, all the other mptcp_send_head() call sites are now under the msk socket lock and we can additionally drop the now unneeded annotation on the transmit head pointer accesses.

Fixes: 6e628cd3a8f7 ("mptcp: use mptcp release_cb for delayed tasks") Cc: stable@vger.kernel.org Signed-off-by: Paolo Abeni pabeni@redhat.com Reviewed-by: Geliang Tang geliang@kernel.org Tested-by: Geliang Tang geliang@kernel.org Reviewed-by: Mat Martineau martineau@kernel.org Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org Link: https://patch.msgid.link/20251028-net-mptcp-send-timeout-v1-1-38ffff5a9ec8@k... Signed-off-by: Jakub Kicinski kuba@kernel.org [ split upstream __subflow_push_pending modification across __mptcp_push_pending and __mptcp_subflow_push_pending ] Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

---

net/mptcp/protocol.c | 13 +++++-------- net/mptcp/protocol.h | 2 +- 2 files changed, 6 insertions(+), 9 deletions(-)

--- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -1137,7 +1137,7 @@ static void __mptcp_clean_una(struct soc if (WARN_ON_ONCE(!msk->recovery)) break;

• 	WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
  

• 	msk->first_pending = mptcp_send_next(sk);
  

  }

dfrag_clear(sk, dfrag); @@ -1674,7 +1674,7 @@ void __mptcp_push_pending(struct sock *s mptcp_update_post_push(msk, dfrag, ret); }

• WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
  

• msk->first_pending = mptcp_send_next(sk);
  

  }

/* at this point we held the socket lock for the last subflow we used */ @@ -1732,7 +1732,7 @@ static void __mptcp_subflow_push_pending mptcp_update_post_push(msk, dfrag, ret); }

• WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
  

• msk->first_pending = mptcp_send_next(sk);
  

  }

out: @@ -1850,7 +1850,7 @@ static int mptcp_sendmsg(struct sock *sk get_page(dfrag->page); list_add_tail(&dfrag->list, &msk->rtx_queue); if (!msk->first_pending)

• 		WRITE_ONCE(msk->first_pending, dfrag);
  

• 		msk->first_pending = dfrag;
  

  } pr_debug("msk=%p dfrag at seq=%llu len=%u sent=%u new=%d\n", msk, dfrag->data_seq, dfrag->data_len, dfrag->already_sent,

@@ -2645,7 +2645,7 @@ static void __mptcp_clear_xmit(struct so struct mptcp_sock *msk = mptcp_sk(sk); struct mptcp_data_frag *dtmp, *dfrag;

• WRITE_ONCE(msk->first_pending, NULL);

• msk->first_pending = NULL; list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list) dfrag_clear(sk, dfrag);

} @@ -3114,9 +3114,6 @@ void __mptcp_data_acked(struct sock *sk) void __mptcp_check_push(struct sock *sk, struct sock *ssk) {

• if (!mptcp_send_head(sk))

• return;
  

• if (!sock_owned_by_user(sk)) { struct sock *xmit_ssk = mptcp_subflow_get_send(mptcp_sk(sk));

--- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -325,7 +325,7 @@ static inline struct mptcp_data_frag *mp { const struct mptcp_sock *msk = mptcp_sk(sk);

• return READ_ONCE(msk->first_pending);

• return msk->first_pending;

} static inline struct mptcp_data_frag *mptcp_send_next(struct sock *sk)

Cheers, Matt