net/sched: act_csum: don't use spinlock in the fast path

use RCU instead of spin_{,unlock}_bh() to protect concurrent read/write on
act_csum configuration, to reduce the effects of contention in the data
path when multiple readers are present.

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

2 files changed, 59 insertions, 15 deletions

diff --git a/include/net/tc_act/tc_csum.h b/include/net/tc_act/tc_csum.h
index 781f3433a0be..9470fd7e4350 100644
--- a/include/net/tc_act/tc_csum.h
+++ b/include/net/tc_act/tc_csum.h
@@ -6,10 +6,16 @@
 #include <net/act_api.h>
 #include <linux/tc_act/tc_csum.h>
 
+struct tcf_csum_params {
+        int action;
+        u32 update_flags;
+        struct rcu_head rcu;
+};
+
 struct tcf_csum {
         struct tc_action common;
 
-        u32 update_flags;
+        struct tcf_csum_params __rcu *params;
 };
 #define to_tcf_csum(a) ((struct tcf_csum *)a)
 
@@ -24,7 +30,13 @@ static inline bool is_tcf_csum(const struct tc_action *a)
 
 static inline u32 tcf_csum_update_flags(const struct tc_action *a)
 {
-        return to_tcf_csum(a)->update_flags;
+        u32 update_flags;
+
+        rcu_read_lock();
+        update_flags = rcu_dereference(to_tcf_csum(a)->params)->update_flags;
+        rcu_read_unlock();
+
+        return update_flags;
 }
 
 #endif /* __NET_TC_CSUM_H */
diff --git a/net/sched/act_csum.c b/net/sched/act_csum.c
index df22da365cd9..b7ba9b06b147 100644
--- a/net/sched/act_csum.c
+++ b/net/sched/act_csum.c
@@ -49,6 +49,7 @@ static int tcf_csum_init(struct net *net, struct nlattr *nla,
                          int bind)
 {
         struct tc_action_net *tn = net_generic(net, csum_net_id);
+        struct tcf_csum_params *params_old, *params_new;
         struct nlattr *tb[TCA_CSUM_MAX + 1];
         struct tc_csum *parm;
         struct tcf_csum *p;
@@ -80,10 +81,21 @@ static int tcf_csum_init(struct net *net, struct nlattr *nla,
         }
 
         p = to_tcf_csum(*a);
-        spin_lock_bh(&p->tcf_lock);
-        p->tcf_action = parm->action;
-        p->update_flags = parm->update_flags;
-        spin_unlock_bh(&p->tcf_lock);
+        ASSERT_RTNL();
+
+        params_new = kzalloc(sizeof(*params_new), GFP_KERNEL);
+        if (unlikely(!params_new)) {
+                if (ret == ACT_P_CREATED)
+                        tcf_idr_release(*a, bind);
+                return -ENOMEM;
+        }
+        params_old = rtnl_dereference(p->params);
+
+        params_new->action = parm->action;
+        params_new->update_flags = parm->update_flags;
+        rcu_assign_pointer(p->params, params_new);
+        if (params_old)
+                kfree_rcu(params_old, rcu);
 
         if (ret == ACT_P_CREATED)
                 tcf_idr_insert(tn, *a);
@@ -539,19 +551,21 @@ static int tcf_csum(struct sk_buff *skb, const struct tc_action *a,
                     struct tcf_result *res)
 {
         struct tcf_csum *p = to_tcf_csum(a);
-        int action;
+        struct tcf_csum_params *params;
         u32 update_flags;
+        int action;
+
+        rcu_read_lock();
+        params = rcu_dereference(p->params);
 
         tcf_lastuse_update(&p->tcf_tm);
         bstats_cpu_update(this_cpu_ptr(p->common.cpu_bstats), skb);
-        spin_lock(&p->tcf_lock);
-        action = p->tcf_action;
-        update_flags = p->update_flags;
-        spin_unlock(&p->tcf_lock);
 
+        action = params->action;
         if (unlikely(action == TC_ACT_SHOT))
-                goto drop;
+                goto drop_stats;
 
+        update_flags = params->update_flags;
         switch (tc_skb_protocol(skb)) {
         case cpu_to_be16(ETH_P_IP):
                 if (!tcf_csum_ipv4(skb, update_flags))
@@ -563,11 +577,16 @@ static int tcf_csum(struct sk_buff *skb, const struct tc_action *a,
                 break;
         }
 
+unlock:
+        rcu_read_unlock();
         return action;
 
 drop:
+        action = TC_ACT_SHOT;
+
+drop_stats:
         qstats_drop_inc(this_cpu_ptr(p->common.cpu_qstats));
-        return TC_ACT_SHOT;
+        goto unlock;
 }
 
 static int tcf_csum_dump(struct sk_buff *skb, struct tc_action *a, int bind,
@@ -575,15 +594,18 @@ static int tcf_csum_dump(struct sk_buff *skb, struct tc_action *a, int bind,
 {
         unsigned char *b = skb_tail_pointer(skb);
         struct tcf_csum *p = to_tcf_csum(a);
+        struct tcf_csum_params *params;
         struct tc_csum opt = {
-                .update_flags = p->update_flags,
                 .index   = p->tcf_index,
-                .action  = p->tcf_action,
                 .refcnt  = p->tcf_refcnt - ref,
                 .bindcnt = p->tcf_bindcnt - bind,
         };
         struct tcf_t t;
 
+        params = rtnl_dereference(p->params);
+        opt.action = params->action;
+        opt.update_flags = params->update_flags;
+
         if (nla_put(skb, TCA_CSUM_PARMS, sizeof(opt), &opt))
                 goto nla_put_failure;
 
@@ -598,6 +620,15 @@ nla_put_failure:
         return -1;
 }
 
+static void tcf_csum_cleanup(struct tc_action *a)
+{
+        struct tcf_csum *p = to_tcf_csum(a);
+        struct tcf_csum_params *params;
+
+        params = rcu_dereference_protected(p->params, 1);
+        kfree_rcu(params, rcu);
+}
+
 static int tcf_csum_walker(struct net *net, struct sk_buff *skb,
                            struct netlink_callback *cb, int type,
                            const struct tc_action_ops *ops)
@@ -621,6 +652,7 @@ static struct tc_action_ops act_csum_ops = {
         .act            = tcf_csum,
         .dump           = tcf_csum_dump,
         .init           = tcf_csum_init,
+        .cleanup        = tcf_csum_cleanup,
         .walk           = tcf_csum_walker,
         .lookup         = tcf_csum_search,
         .size           = sizeof(struct tcf_csum),