mptcp: decouple mptcp fastclose from tcp close

With the current fastclose implementation, the mptcp_do_fastclose()
helper is in charge of two distinct actions: send the fastclose reset
and cleanup the subflows.

Formally decouple the two steps, ensuring that mptcp explicitly closes
all the subflows after the mentioned helper.

This will make the upcoming fix simpler, and allows dropping the 2nd
argument from mptcp_destroy_common(). The Fixes tag is then the same as
in the next commit to help with the backports.

Fixes: d21f834 ("mptcp: use fastclose on more edge scenarios")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Geliang Tang <geliang@kernel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251118-net-mptcp-misc-fixes-6-18-rc6-v1-5-806d3781c95f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Paolo Abeni

net/mptcp/protocol.c

@@ -2808,7 +2808,11 @@ static void mptcp_worker(struct work_struct *work)
 		__mptcp_close_subflow(sk);
 
 	if (mptcp_close_tout_expired(sk)) {
+		struct mptcp_subflow_context *subflow, *tmp;
+
 		mptcp_do_fastclose(sk);
+		mptcp_for_each_subflow_safe(msk, subflow, tmp)
+			__mptcp_close_ssk(sk, subflow->tcp_sock, subflow, 0);
 		mptcp_close_wake_up(sk);
 	}
 
@@ -3233,7 +3237,8 @@ static int mptcp_disconnect(struct sock *sk, int flags)
 	/* msk->subflow is still intact, the following will not free the first
 	 * subflow
 	 */
-	mptcp_destroy_common(msk, MPTCP_CF_FASTCLOSE);
+	mptcp_do_fastclose(sk);
+	mptcp_destroy_common(msk);
 
 	/* The first subflow is already in TCP_CLOSE status, the following
 	 * can't overlap with a fallback anymore
@@ -3412,7 +3417,7 @@ void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk)
 		msk->rcvq_space.space = TCP_INIT_CWND * TCP_MSS_DEFAULT;
 }
 
-void mptcp_destroy_common(struct mptcp_sock *msk, unsigned int flags)
+void mptcp_destroy_common(struct mptcp_sock *msk)
 {
 	struct mptcp_subflow_context *subflow, *tmp;
 	struct sock *sk = (struct sock *)msk;
@@ -3421,7 +3426,7 @@ void mptcp_destroy_common(struct mptcp_sock *msk, unsigned int flags)
 
 	/* join list will be eventually flushed (with rst) at sock lock release time */
 	mptcp_for_each_subflow_safe(msk, subflow, tmp)
-		__mptcp_close_ssk(sk, mptcp_subflow_tcp_sock(subflow), subflow, flags);
+		__mptcp_close_ssk(sk, mptcp_subflow_tcp_sock(subflow), subflow, 0);
 
 	__skb_queue_purge(&sk->sk_receive_queue);
 	skb_rbtree_purge(&msk->out_of_order_queue);
@@ -3439,7 +3444,7 @@ static void mptcp_destroy(struct sock *sk)
 
 	/* allow the following to close even the initial subflow */
 	msk->free_first = 1;
-	mptcp_destroy_common(msk, 0);
+	mptcp_destroy_common(msk);
 	sk_sockets_allocated_dec(sk);
 }
 

net/mptcp/protocol.h

@@ -977,7 +977,7 @@ static inline void mptcp_propagate_sndbuf(struct sock *sk, struct sock *ssk)
 	local_bh_enable();
 }
 
-void mptcp_destroy_common(struct mptcp_sock *msk, unsigned int flags);
+void mptcp_destroy_common(struct mptcp_sock *msk);
 
 #define MPTCP_TOKEN_MAX_RETRIES	4