FAILED: patch "[PATCH] mptcp: reset fallback status gracefully at disconnect() time" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-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 <[email protected]>.

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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x da9b2fc7b73d147d88abe1922de5ab72d72d7756
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025072114-latch-paralysis-ee70@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From da9b2fc7b73d147d88abe1922de5ab72d72d7756 Mon Sep 17 00:00:00 2001
From: Paolo Abeni <[email protected]>
Date: Mon, 14 Jul 2025 18:41:46 +0200
Subject: [PATCH] mptcp: reset fallback status gracefully at disconnect() time

mptcp_disconnect() clears the fallback bit unconditionally, without touching the associated flags.

The bit clear is safe, as no fallback operation can race with that -- all subflow are already in TCP_CLOSE status thanks to the previous FASTCLOSE -- but we need to consistently reset all the fallback related status.

Also acquire the relevant lock, to avoid fouling static analyzers.

index bf92cee9b5ce..6a817a13b154 100644
@@ -3142,7 +3142,16 @@ static int mptcp_disconnect(struct sock *sk, int flags)
 	 * subflow
 	 */
 	mptcp_destroy_common(msk, MPTCP_CF_FASTCLOSE);
+
+	/* The first subflow is already in TCP_CLOSE status, the following
+	 * can't overlap with a fallback anymore
+	 */
+	spin_lock_bh(&msk->fallback_lock);
+	msk->allow_subflows = true;
+	msk->allow_infinite_fallback = true;
 	WRITE_ONCE(msk->flags, 0);
+	spin_unlock_bh(&msk->fallback_lock);
+
 	msk->cb_flags = 0;
 	msk->recovery = false;
 	WRITE_ONCE(msk->can_ack, false);