net: sched: act_sample: remove dependency on rtnl lock

Use tcf spinlock to protect private sample action data from concurrent
modification during dump and init.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_sample.c

@@ -80,11 +80,13 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
 	}
 	s = to_sample(*a);
 
+	spin_lock(&s->tcf_lock);
 	s->tcf_action = parm->action;
 	s->rate = nla_get_u32(tb[TCA_SAMPLE_RATE]);
 	s->psample_group_num = nla_get_u32(tb[TCA_SAMPLE_PSAMPLE_GROUP]);
 	psample_group = psample_group_get(net, s->psample_group_num);
 	if (!psample_group) {
+		spin_unlock(&s->tcf_lock);
 		tcf_idr_release(*a, bind);
 		return -ENOMEM;
 	}
@@ -94,6 +96,7 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
 		s->truncate = true;
 		s->trunc_size = nla_get_u32(tb[TCA_SAMPLE_TRUNC_SIZE]);
 	}
+	spin_unlock(&s->tcf_lock);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
@@ -105,7 +108,8 @@ static void tcf_sample_cleanup(struct tc_action *a)
 	struct tcf_sample *s = to_sample(a);
 	struct psample_group *psample_group;
 
-	psample_group = rtnl_dereference(s->psample_group);
+	/* last reference to action, no need to lock */
+	psample_group = rcu_dereference_protected(s->psample_group, 1);
 	RCU_INIT_POINTER(s->psample_group, NULL);
 	if (psample_group)
 		psample_group_put(psample_group);
@@ -174,12 +178,13 @@ static int tcf_sample_dump(struct sk_buff *skb, struct tc_action *a,
 	struct tcf_sample *s = to_sample(a);
 	struct tc_sample opt = {
 		.index      = s->tcf_index,
-		.action     = s->tcf_action,
 		.refcnt     = refcount_read(&s->tcf_refcnt) - ref,
 		.bindcnt    = atomic_read(&s->tcf_bindcnt) - bind,
 	};
 	struct tcf_t t;
 
+	spin_lock(&s->tcf_lock);
+	opt.action = s->tcf_action;
 	if (nla_put(skb, TCA_SAMPLE_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
 
@@ -196,9 +201,12 @@ static int tcf_sample_dump(struct sk_buff *skb, struct tc_action *a,
 
 	if (nla_put_u32(skb, TCA_SAMPLE_PSAMPLE_GROUP, s->psample_group_num))
 		goto nla_put_failure;
+	spin_unlock(&s->tcf_lock);
+
 	return skb->len;
 
 nla_put_failure:
+	spin_unlock(&s->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }