FAILED: patch "[PATCH] mptcp: pm: re-using ID of unused removed subflows" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

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 edd8b5d868a4d459f3065493001e293901af758d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024082612-hydrated-overdress-ea6a@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

edd8b5d868a4 ("mptcp: pm: re-using ID of unused removed subflows")
d045b9eb95a9 ("mptcp: introduce implicit endpoints")
33397b83eee6 ("selftests: mptcp: add backup with port testcase")
09f12c3ab7a5 ("mptcp: allow to use port and non-signal in set_flags")
6a0653b96f5d ("selftests: mptcp: add fullmesh setting tests")
327b9a94e2a8 ("selftests: mptcp: more stable join tests-cases")

thanks,

greg k-h

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

From edd8b5d868a4d459f3065493001e293901af758d Mon Sep 17 00:00:00 2001
From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Date: Mon, 19 Aug 2024 21:45:21 +0200
Subject: [PATCH] mptcp: pm: re-using ID of unused removed subflows

If no subflow is attached to the 'subflow' endpoint that is being
removed, the addr ID will not be marked as available again.

Mark the linked ID as available when removing the 'subflow' endpoint if
no subflow is attached to it.

While at it, the local_addr_used counter is decremented if the ID was
marked as being used to reflect the reality, but also to allow adding
new endpoints after that.

Fixes: b6c08380860b ("mptcp: remove addr and subflow in PM netlink")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-3-38035d40de5b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 26f0329e16bb..8b232a210a06 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1469,8 +1469,17 @@ static int mptcp_nl_remove_subflow_and_signal_addr(struct net *net,
 		remove_subflow = lookup_subflow_by_saddr(&msk->conn_list, addr);
 		mptcp_pm_remove_anno_addr(msk, addr, remove_subflow &&
 					  !(entry->flags & MPTCP_PM_ADDR_FLAG_IMPLICIT));
-		if (remove_subflow)
+
+		if (remove_subflow) {
 			mptcp_pm_remove_subflow(msk, &list);
+		} else if (entry->flags & MPTCP_PM_ADDR_FLAG_SUBFLOW) {
+			/* If the subflow has been used, but now closed */
+			spin_lock_bh(&msk->pm.lock);
+			if (!__test_and_set_bit(entry->addr.id, msk->pm.id_avail_bitmap))
+				msk->pm.local_addr_used--;
+			spin_unlock_bh(&msk->pm.lock);
+		}
+
 		release_sock(sk);
 
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