Merge branch 'mptcp-subflow-accounting-fix'

Mat Martineau says:

====================
mptcp: Subflow accounting fix

This series contains a bug fix affecting the in-kernel path manager
(patch 1), where closing subflows would sometimes not adjust the PM's
count of active subflows. Patch 2 updates the selftests to exercise the
new code.
====================

Link: https://lore.kernel.org/r/20220512232642.541301-1-mathew.j.martineau@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

4 files changed, 71 insertions, 8 deletions

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 01809eef29b4..aa51b100e033 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -178,14 +178,13 @@ void mptcp_pm_subflow_check_next(struct mptcp_sock *msk, const struct sock *ssk,
 	struct mptcp_pm_data *pm = &msk->pm;
 	bool update_subflows;
 
-	update_subflows = (ssk->sk_state == TCP_CLOSE) &&
-			  (subflow->request_join || subflow->mp_join);
+	update_subflows = subflow->request_join || subflow->mp_join;
 	if (!READ_ONCE(pm->work_pending) && !update_subflows)
 		return;
 
 	spin_lock_bh(&pm->lock);
 	if (update_subflows)
-		pm->subflows--;
+		__mptcp_pm_close_subflow(msk);
 
 	/* Even if this subflow is not really established, tell the PM to try
 	 * to pick the next ones, if possible.
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 3c1a3036550f..f4ce28bb0fdc 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -833,6 +833,20 @@ unsigned int mptcp_pm_get_add_addr_accept_max(const struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_subflows_max(const struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_local_addr_max(const struct mptcp_sock *msk);
 
+/* called under PM lock */
+static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk)
+{
+	if (--msk->pm.subflows < mptcp_pm_get_subflows_max(msk))
+		WRITE_ONCE(msk->pm.accept_subflow, true);
+}
+
+static inline void mptcp_pm_close_subflow(struct mptcp_sock *msk)
+{
+	spin_lock_bh(&msk->pm.lock);
+	__mptcp_pm_close_subflow(msk);
+	spin_unlock_bh(&msk->pm.lock);
+}
+
 void mptcp_sockopt_sync(struct mptcp_sock *msk, struct sock *ssk);
 void mptcp_sockopt_sync_locked(struct mptcp_sock *msk, struct sock *ssk);
 
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index aba260f547da..8c37087f0d84 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1422,20 +1422,20 @@ int __mptcp_subflow_connect(struct sock *sk, const struct mptcp_addr_info *loc,
 	struct sockaddr_storage addr;
 	int remote_id = remote->id;
 	int local_id = loc->id;
+	int err = -ENOTCONN;
 	struct socket *sf;
 	struct sock *ssk;
 	u32 remote_token;
 	int addrlen;
 	int ifindex;
 	u8 flags;
-	int err;
 
 	if (!mptcp_is_fully_established(sk))
-		return -ENOTCONN;
+		goto err_out;
 
 	err = mptcp_subflow_create_socket(sk, &sf);
 	if (err)
-		return err;
+		goto err_out;
 
 	ssk = sf->sk;
 	subflow = mptcp_subflow_ctx(ssk);
@@ -1492,6 +1492,12 @@ failed_unlink:
 failed:
 	subflow->disposable = 1;
 	sock_release(sf);
+
+err_out:
+	/* we account subflows before the creation, and this failures will not
+	 * be caught by sk_state_change()
+	 */
+	mptcp_pm_close_subflow(msk);
 	return err;
 }
 
diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 7314257d248a..48ef112f42c2 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -1444,6 +1444,33 @@ chk_prio_nr()
 	[ "${dump_stats}" = 1 ] && dump_stats
 }
 
+chk_subflow_nr()
+{
+	local need_title="$1"
+	local msg="$2"
+	local subflow_nr=$3
+	local cnt1
+	local cnt2
+
+	if [ -n "${need_title}" ]; then
+		printf "%03u %-36s %s" "${TEST_COUNT}" "${TEST_NAME}" "${msg}"
+	else
+		printf "%-${nr_blank}s %s" " " "${msg}"
+	fi
+
+	cnt1=$(ss -N $ns1 -tOni | grep -c token)
+	cnt2=$(ss -N $ns2 -tOni | grep -c token)
+	if [ "$cnt1" != "$subflow_nr" -o "$cnt2" != "$subflow_nr" ]; then
+		echo "[fail] got $cnt1:$cnt2 subflows expected $subflow_nr"
+		fail_test
+		dump_stats=1
+	else
+		echo "[ ok ]"
+	fi
+
+	[ "${dump_stats}" = 1 ] && ( ss -N $ns1 -tOni ; ss -N $ns1 -tOni | grep token; ip -n $ns1 mptcp endpoint )
+}
+
 chk_link_usage()
 {
 	local ns=$1
@@ -2556,7 +2583,7 @@ fastclose_tests()
 	fi
 }
 
-implicit_tests()
+endpoint_tests()
 {
 	# userspace pm type prevents add_addr
 	if reset "implicit EP"; then
@@ -2578,6 +2605,23 @@ implicit_tests()
 			$ns2 10.0.2.2 id 1 flags signal
 		wait
 	fi
+
+	if reset "delete and re-add"; then
+		pm_nl_set_limits $ns1 1 1
+		pm_nl_set_limits $ns2 1 1
+		pm_nl_add_endpoint $ns2 10.0.2.2 id 2 dev ns2eth2 flags subflow
+		run_tests $ns1 $ns2 10.0.1.1 4 0 0 slow &
+
+		wait_mpj $ns2
+		pm_nl_del_endpoint $ns2 2 10.0.2.2
+		sleep 0.5
+		chk_subflow_nr needtitle "after delete" 1
+
+		pm_nl_add_endpoint $ns2 10.0.2.2 dev ns2eth2 flags subflow
+		wait_mpj $ns2
+		chk_subflow_nr "" "after re-add" 2
+		wait
+	fi
 }
 
 # [$1: error message]
@@ -2624,7 +2668,7 @@ all_tests_sorted=(
 	d@deny_join_id0_tests
 	m@fullmesh_tests
 	z@fastclose_tests
-	I@implicit_tests
+	I@endpoint_tests
 )
 
 all_tests_args=""