commit b6a66e521a2032f7fcba2af5a9bcbaeaa19b7ca3 upstream.

The 'mptcp_subflow_context' structure has two items related to the
backup flags:

 - 'backup': the subflow has been marked as backup by the other peer

 - 'request_bkup': the backup flag has been set by the host

Before this patch, the scheduler was only looking at the 'backup' flag.
That can make sense in some cases, but it looks like that's not what we
wanted for the general use, because either the path-manager was setting
both of them when sending an MP_PRIO, or the receiver was duplicating
the 'backup' flag in the subflow request.

Note that the use of these two flags in the path-manager are going to be
fixed in the next commits, but this change here is needed not to modify
the behaviour.

Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ Conflicts in protocol.c, because the context has changed in commit
  3ce0852c86b9 ("mptcp: enforce HoL-blocking estimation"), which is not
  in this version. This commit is unrelated to this modification. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 include/trace/events/mptcp.h |  2 +-
 net/mptcp/protocol.c         | 10 ++++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/mptcp.h b/include/trace/events/mptcp.h
index 6bf43176f14c..df26c1dd3d8d 100644
--- a/include/trace/events/mptcp.h
+++ b/include/trace/events/mptcp.h
@@ -34,7 +34,7 @@ TRACE_EVENT(mptcp_subflow_get_send,
 		struct sock *ssk;
 
 		__entry->active = mptcp_subflow_active(subflow);
-		__entry->backup = subflow->backup;
+		__entry->backup = subflow->backup || subflow->request_bkup;
 
 		if (subflow->tcp_sock && sk_fullsock(subflow->tcp_sock))
 			__entry->free = sk_stream_memory_free(subflow->tcp_sock);
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 081c8d00472d..b6b708dbfce9 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1514,13 +1514,15 @@ static struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
 		send_info[i].ratio = -1;
 	}
 	mptcp_for_each_subflow(msk, subflow) {
+		bool backup = subflow->backup || subflow->request_bkup;
+
 		trace_mptcp_subflow_get_send(subflow);
 		ssk =  mptcp_subflow_tcp_sock(subflow);
 		if (!mptcp_subflow_active(subflow))
 			continue;
 
 		tout = max(tout, mptcp_timeout_from_subflow(subflow));
-		nr_active += !subflow->backup;
+		nr_active += !backup;
 		if (!sk_stream_memory_free(subflow->tcp_sock) || !tcp_sk(ssk)->snd_wnd)
 			continue;
 
@@ -1530,9 +1532,9 @@ static struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
 
 		ratio = div_u64((u64)READ_ONCE(ssk->sk_wmem_queued) << 32,
 				pace);
-		if (ratio < send_info[subflow->backup].ratio) {
-			send_info[subflow->backup].ssk = ssk;
-			send_info[subflow->backup].ratio = ratio;
+		if (ratio < send_info[backup].ratio) {
+			send_info[backup].ssk = ssk;
+			send_info[backup].ratio = ratio;
 		}
 	}
 	__mptcp_set_timeout(sk, tout);
-- 
2.45.2

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

    mptcp: sched: check both directions for backup

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mptcp-sched-check-both-directions-for-backup.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.


From matttbe@kernel.org Fri Aug  9 11:05:44 2024
From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Date: Fri,  9 Aug 2024 11:05:31 +0200
Subject: mptcp: sched: check both directions for backup
To: stable@vger.kernel.org, gregkh@linuxfoundation.org
Cc: MPTCP Upstream <mptcp@lists.linux.dev>, "Matthieu Baerts (NGI0)" <matttbe@kernel.org>, Mat Martineau <martineau@kernel.org>, Paolo Abeni <pabeni@redhat.com>
Message-ID: <20240809090530.2696742-2-matttbe@kernel.org>

From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>

commit b6a66e521a2032f7fcba2af5a9bcbaeaa19b7ca3 upstream.

The 'mptcp_subflow_context' structure has two items related to the
backup flags:

 - 'backup': the subflow has been marked as backup by the other peer

 - 'request_bkup': the backup flag has been set by the host

Before this patch, the scheduler was only looking at the 'backup' flag.
That can make sense in some cases, but it looks like that's not what we
wanted for the general use, because either the path-manager was setting
both of them when sending an MP_PRIO, or the receiver was duplicating
the 'backup' flag in the subflow request.

Note that the use of these two flags in the path-manager are going to be
fixed in the next commits, but this change here is needed not to modify
the behaviour.

Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ Conflicts in protocol.c, because the context has changed in commit
  3ce0852c86b9 ("mptcp: enforce HoL-blocking estimation"), which is not
  in this version. This commit is unrelated to this modification. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/trace/events/mptcp.h |    2 +-
 net/mptcp/protocol.c         |   10 ++++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

--- a/include/trace/events/mptcp.h
+++ b/include/trace/events/mptcp.h
@@ -34,7 +34,7 @@ TRACE_EVENT(mptcp_subflow_get_send,
 		struct sock *ssk;
 
 		__entry->active = mptcp_subflow_active(subflow);
-		__entry->backup = subflow->backup;
+		__entry->backup = subflow->backup || subflow->request_bkup;
 
 		if (subflow->tcp_sock && sk_fullsock(subflow->tcp_sock))
 			__entry->free = sk_stream_memory_free(subflow->tcp_sock);
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1514,13 +1514,15 @@ static struct sock *mptcp_subflow_get_se
 		send_info[i].ratio = -1;
 	}
 	mptcp_for_each_subflow(msk, subflow) {
+		bool backup = subflow->backup || subflow->request_bkup;
+
 		trace_mptcp_subflow_get_send(subflow);
 		ssk =  mptcp_subflow_tcp_sock(subflow);
 		if (!mptcp_subflow_active(subflow))
 			continue;
 
 		tout = max(tout, mptcp_timeout_from_subflow(subflow));
-		nr_active += !subflow->backup;
+		nr_active += !backup;
 		if (!sk_stream_memory_free(subflow->tcp_sock) || !tcp_sk(ssk)->snd_wnd)
 			continue;
 
@@ -1530,9 +1532,9 @@ static struct sock *mptcp_subflow_get_se
 
 		ratio = div_u64((u64)READ_ONCE(ssk->sk_wmem_queued) << 32,
 				pace);
-		if (ratio < send_info[subflow->backup].ratio) {
-			send_info[subflow->backup].ssk = ssk;
-			send_info[subflow->backup].ratio = ratio;
+		if (ratio < send_info[backup].ratio) {
+			send_info[backup].ssk = ssk;
+			send_info[backup].ratio = ratio;
 		}
 	}
 	__mptcp_set_timeout(sk, tout);


Patches currently in stable-queue which might be from matttbe@kernel.org are

queue-5.15/mptcp-fix-nl-pm-announced-address-accounting.patch
queue-5.15/mptcp-distinguish-rcv-vs-sent-backup-flag-in-requests.patch
queue-5.15/mptcp-pm-fix-backup-support-in-signal-endpoints.patch
queue-5.15/mptcp-mib-count-mpj-with-backup-flag.patch
queue-5.15/selftests-mptcp-join-check-backup-support-in-signal-endp.patch
queue-5.15/selftests-mptcp-join-validate-backup-in-mpj.patch
queue-5.15/mptcp-sched-check-both-directions-for-backup.patch
queue-5.15/mptcp-export-local_address.patch
queue-5.15/mptcp-pm-only-set-request_bkup-flag-when-sending-mp_prio.patch
queue-5.15/mptcp-fix-bad-rcvpruned-mib-accounting.patch
queue-5.15/mptcp-fix-duplicate-data-handling.patch