mptcp: drop the push_pending field

Such field is there to avoid acquiring the data lock in a few spots,
but it adds complexity to the already non trivial locking schema.

All the relevant call sites (mptcp-level re-injection, set socket
options), are slow-path, drop such field in favor of 'cb_flags', adding
the relevant locking.

This patch could be seen as an improvement, instead of a fix. But it
simplifies the next patch. The 'Fixes' tag has been added to help having
this series backported to stable.

Fixes: e9d09ba ("mptcp: avoid atomic bit manipulation when possible")
Cc: [email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Reviewed-by: Mat Martineau <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

net/mptcp/protocol.c

@@ -1505,8 +1505,11 @@ static void mptcp_update_post_push(struct mptcp_sock *msk,
 
 void mptcp_check_and_set_pending(struct sock *sk)
 {
-	if (mptcp_send_head(sk))
-		mptcp_sk(sk)->push_pending |= BIT(MPTCP_PUSH_PENDING);
+	if (mptcp_send_head(sk)) {
+		mptcp_data_lock(sk);
+		mptcp_sk(sk)->cb_flags |= BIT(MPTCP_PUSH_PENDING);
+		mptcp_data_unlock(sk);
+	}
 }
 
 static int __subflow_push_pending(struct sock *sk, struct sock *ssk,
@@ -3142,7 +3145,6 @@ static int mptcp_disconnect(struct sock *sk, int flags)
 	mptcp_destroy_common(msk, MPTCP_CF_FASTCLOSE);
 	WRITE_ONCE(msk->flags, 0);
 	msk->cb_flags = 0;
-	msk->push_pending = 0;
 	msk->recovery = false;
 	msk->can_ack = false;
 	msk->fully_established = false;
@@ -3330,8 +3332,7 @@ static void mptcp_release_cb(struct sock *sk)
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
 	for (;;) {
-		unsigned long flags = (msk->cb_flags & MPTCP_FLAGS_PROCESS_CTX_NEED) |
-				      msk->push_pending;
+		unsigned long flags = (msk->cb_flags & MPTCP_FLAGS_PROCESS_CTX_NEED);
 		struct list_head join_list;
 
 		if (!flags)
@@ -3347,7 +3348,6 @@ static void mptcp_release_cb(struct sock *sk)
 		 *    datapath acquires the msk socket spinlock while helding
 		 *    the subflow socket lock
 		 */
-		msk->push_pending = 0;
 		msk->cb_flags &= ~flags;
 		spin_unlock_bh(&sk->sk_lock.slock);
 

net/mptcp/protocol.h

@@ -286,7 +286,6 @@ struct mptcp_sock {
 	int		rmem_released;
 	unsigned long	flags;
 	unsigned long	cb_flags;
-	unsigned long	push_pending;
 	bool		recovery;		/* closing subflow write queue reinjected */
 	bool		can_ack;
 	bool		fully_established;