net/sched: act_skbedit: don't use spinlock in the data path

use RCU instead of spin_{,un}lock_bh, to protect concurrent read/write on
act_skbedit configuration. This reduces the effects of contention in the
data path, in case multiple readers are present.

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tc_act/tc_skbedit.h

@@ -22,14 +22,19 @@
 #include <net/act_api.h>
 #include <linux/tc_act/tc_skbedit.h>
 
+struct tcf_skbedit_params {
+	u32 flags;
+	u32 priority;
+	u32 mark;
+	u32 mask;
+	u16 queue_mapping;
+	u16 ptype;
+	struct rcu_head rcu;
+};
+
 struct tcf_skbedit {
-	struct tc_action	common;
-	u32		flags;
-	u32		priority;
-	u32		mark;
-	u32		mask;
-	u16		queue_mapping;
-	u16		ptype;
+	struct tc_action common;
+	struct tcf_skbedit_params __rcu *params;
 };
 #define to_skbedit(a) ((struct tcf_skbedit *)a)
 
@@ -37,15 +42,27 @@ struct tcf_skbedit {
 static inline bool is_tcf_skbedit_mark(const struct tc_action *a)
 {
 #ifdef CONFIG_NET_CLS_ACT
-	if (a->ops && a->ops->type == TCA_ACT_SKBEDIT)
-		return to_skbedit(a)->flags == SKBEDIT_F_MARK;
+	u32 flags;
+
+	if (a->ops && a->ops->type == TCA_ACT_SKBEDIT) {
+		rcu_read_lock();
+		flags = rcu_dereference(to_skbedit(a)->params)->flags;
+		rcu_read_unlock();
+		return flags == SKBEDIT_F_MARK;
+	}
 #endif
 	return false;
 }
 
 static inline u32 tcf_skbedit_mark(const struct tc_action *a)
 {
-	return to_skbedit(a)->mark;
+	u32 mark;
+
+	rcu_read_lock();
+	mark = rcu_dereference(to_skbedit(a)->params)->mark;
+	rcu_read_unlock();
+
+	return mark;
 }
 
 #endif /* __NET_TC_SKBEDIT_H */