mptcp: Use nested-BH locking for hmac_storage

mptcp_delegated_actions is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT this data
structure requires explicit locking.

Add a local_lock_t to the data structure and use local_lock_nested_bh() for
locking. This change adds only lockdep coverage and does not alter the
functional behaviour for !PREEMPT_RT.

Cc: Matthieu Baerts <[email protected]>
Cc: Mat Martineau <[email protected]>
Cc: Geliang Tang <[email protected]>
Cc: [email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: Sebastian Andrzej Siewior

net/mptcp/protocol.c

@@ -46,7 +46,9 @@ static struct percpu_counter mptcp_sockets_allocated ____cacheline_aligned_in_sm
 static void __mptcp_destroy_sock(struct sock *sk);
 static void mptcp_check_send_data_fin(struct sock *sk);
 
-DEFINE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
+DEFINE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions) = {
+	.bh_lock = INIT_LOCAL_LOCK(bh_lock),
+};
 static struct net_device *mptcp_napi_dev;
 
 /* Returns end sequence number of the receiver's advertised window */

net/mptcp/protocol.h

@@ -479,6 +479,7 @@ mptcp_subflow_rsk(const struct request_sock *rsk)
 
 struct mptcp_delegated_action {
 	struct napi_struct napi;
+	local_lock_t bh_lock;
 	struct list_head head;
 };
 
@@ -670,9 +671,11 @@ static inline void mptcp_subflow_delegate(struct mptcp_subflow_context *subflow,
 		if (WARN_ON_ONCE(!list_empty(&subflow->delegated_node)))
 			return;
 
+		local_lock_nested_bh(&mptcp_delegated_actions.bh_lock);
 		delegated = this_cpu_ptr(&mptcp_delegated_actions);
 		schedule = list_empty(&delegated->head);
 		list_add_tail(&subflow->delegated_node, &delegated->head);
+		local_unlock_nested_bh(&mptcp_delegated_actions.bh_lock);
 		sock_hold(mptcp_subflow_tcp_sock(subflow));
 		if (schedule)
 			napi_schedule(&delegated->napi);
@@ -684,11 +687,15 @@ mptcp_subflow_delegated_next(struct mptcp_delegated_action *delegated)
 {
 	struct mptcp_subflow_context *ret;
 
-	if (list_empty(&delegated->head))
+	local_lock_nested_bh(&mptcp_delegated_actions.bh_lock);
+	if (list_empty(&delegated->head)) {
+		local_unlock_nested_bh(&mptcp_delegated_actions.bh_lock);
 		return NULL;
+	}
 
 	ret = list_first_entry(&delegated->head, struct mptcp_subflow_context, delegated_node);
 	list_del_init(&ret->delegated_node);
+	local_unlock_nested_bh(&mptcp_delegated_actions.bh_lock);
 	return ret;
 }