netdev - [PATCH net-next 15/18] mptcp: Use nested-BH locking for hmac

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Message-ID: <20250309144653.825351-16-bigeasy@linutronix.de>
Date: Sun,  9 Mar 2025 15:46:50 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: netdev@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Matthieu Baerts <matttbe@...nel.org>,
	Mat Martineau <martineau@...nel.org>,
	Geliang Tang <geliang@...nel.org>,
	mptcp@...ts.linux.dev
Subject: [PATCH net-next 15/18] 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 <matttbe@...nel.org>
Cc: Mat Martineau <martineau@...nel.org>
Cc: Geliang Tang <geliang@...nel.org>
Cc: mptcp@...ts.linux.dev
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/mptcp/protocol.c | 4 +++-
 net/mptcp/protocol.h | 9 ++++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 6bd8190474706..922b5baf3372a 100644
--- a/net/mptcp/protocol.c
+++ b/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 */
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index ad21925af0612..8705d699e9870 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -480,6 +480,7 @@ 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;
 };
 
@@ -671,9 +672,11 @@ 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);
@@ -685,11 +688,15 @@ 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;
 }
 
-- 
2.47.2