netdev - [PATCH net-next 13/18] net/sched: act_mirred: Move the recursion counter struct netdev

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Message-ID: <20250309144653.825351-14-bigeasy@linutronix.de>
Date: Sun,  9 Mar 2025 15:46:48 +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>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>
Subject: [PATCH net-next 13/18] net/sched: act_mirred: Move the recursion counter struct netdev_xmit.

mirred_nest_level 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.

Move mirred_nest_level to struct netdev_xmit as u8, provide wrappers.

Cc: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Jiri Pirko <jiri@...nulli.us>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 include/linux/netdevice_xmit.h |  3 +++
 net/sched/act_mirred.c         | 28 +++++++++++++++++++++++++---
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/include/linux/netdevice_xmit.h b/include/linux/netdevice_xmit.h
index 3bbbc1a9860a3..4793ec42b1faa 100644
--- a/include/linux/netdevice_xmit.h
+++ b/include/linux/netdevice_xmit.h
@@ -11,6 +11,9 @@ struct netdev_xmit {
 #if IS_ENABLED(CONFIG_NF_DUP_NETDEV)
 	u8 nf_dup_skb_recursion;
 #endif
+#if IS_ENABLED(CONFIG_NET_ACT_MIRRED)
+	u8 sched_mirred_nest;
+#endif
 };
 
 #endif
diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index 5b38143659249..8d8cfac6cc6af 100644
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -30,7 +30,29 @@ static LIST_HEAD(mirred_list);
 static DEFINE_SPINLOCK(mirred_list_lock);
 
 #define MIRRED_NEST_LIMIT    4
-static DEFINE_PER_CPU(unsigned int, mirred_nest_level);
+
+#ifndef CONFIG_PREEMPT_RT
+static u8 tcf_mirred_nest_level_inc_return(void)
+{
+	return __this_cpu_inc_return(softnet_data.xmit.sched_mirred_nest);
+}
+
+static void tcf_mirred_nest_level_dec(void)
+{
+	__this_cpu_dec(softnet_data.xmit.sched_mirred_nest);
+}
+
+#else
+static u8 tcf_mirred_nest_level_inc_return(void)
+{
+	return current->net_xmit.nf_dup_skb_recursion++;
+}
+
+static void tcf_mirred_nest_level_dec(void)
+{
+	current->net_xmit.nf_dup_skb_recursion--;
+}
+#endif
 
 static bool tcf_mirred_is_act_redirect(int action)
 {
@@ -423,7 +445,7 @@ TC_INDIRECT_SCOPE int tcf_mirred_act(struct sk_buff *skb,
 	int m_eaction;
 	u32 blockid;
 
-	nest_level = __this_cpu_inc_return(mirred_nest_level);
+	nest_level = tcf_mirred_nest_level_inc_return();
 	if (unlikely(nest_level > MIRRED_NEST_LIMIT)) {
 		net_warn_ratelimited("Packet exceeded mirred recursion limit on dev %s\n",
 				     netdev_name(skb->dev));
@@ -454,7 +476,7 @@ TC_INDIRECT_SCOPE int tcf_mirred_act(struct sk_buff *skb,
 				   retval);
 
 dec_nest_level:
-	__this_cpu_dec(mirred_nest_level);
+	tcf_mirred_nest_level_dec();
 
 	return retval;
 }
-- 
2.47.2