netdev - [PATCH net-next 11/18] openvswitch: Use nested-BH locking for ovs

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Message-ID: <20250309144653.825351-12-bigeasy@linutronix.de>
Date: Sun,  9 Mar 2025 15:46:46 +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>,
	Pravin B Shelar <pshelar@....org>,
	dev@...nvswitch.org
Subject: [PATCH net-next 11/18] openvswitch: Use nested-BH locking for ovs_actions.

ovs_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.
The data structure can be referenced recursive and there is a recursion
counter to avoid too many recursions.

Add a local_lock_t to the data structure and use
local_lock_nested_bh() for locking. Add an owner of the struct which is
the current task and acquire the lock only if the structure is not owned
by the current task.

Cc: Pravin B Shelar <pshelar@....org>
Cc: dev@...nvswitch.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/openvswitch/actions.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index 322ca7b30c3bc..c4131e04c1284 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -82,6 +82,8 @@ struct ovs_action {
 	struct action_fifo action_fifos;
 	struct action_flow_keys flow_keys;
 	int exec_level;
+	struct task_struct *owner;
+	local_lock_t bh_lock;
 };
 
 static DEFINE_PER_CPU(struct ovs_action, ovs_actions);
@@ -1690,8 +1692,14 @@ int ovs_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			const struct sw_flow_actions *acts,
 			struct sw_flow_key *key)
 {
+	struct ovs_action *ovs_act = this_cpu_ptr(&ovs_actions);
 	int err, level;
 
+	if (ovs_act->owner != current) {
+		local_lock_nested_bh(&ovs_actions.bh_lock);
+		ovs_act->owner = current;
+	}
+
 	level = __this_cpu_inc_return(ovs_actions.exec_level);
 	if (unlikely(level > OVS_RECURSION_LIMIT)) {
 		net_crit_ratelimited("ovs: recursion limit reached on datapath %s, probable configuration error\n",
@@ -1710,5 +1718,10 @@ int ovs_execute_actions(struct datapath *dp, struct sk_buff *skb,
 
 out:
 	__this_cpu_dec(ovs_actions.exec_level);
+
+	if (level == 1) {
+		ovs_act->owner = NULL;
+		local_unlock_nested_bh(&ovs_actions.bh_lock);
+	}
 	return err;
 }
-- 
2.47.2