ip6mr: ip6mr_cache_report() changes

ip6mr_cache_report() first argument can be marked const, and we change
the caller convention about which lock needs to be held.

Instead of read_lock(&mrt_lock), we can use rcu_read_lock().
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6mr.c

@@ -91,11 +91,11 @@ static void ip6mr_free_table(struct mr_table *mrt);
 static void ip6_mr_forward(struct net *net, struct mr_table *mrt,
 			   struct net_device *dev, struct sk_buff *skb,
 			   struct mfc6_cache *cache);
-static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
+static int ip6mr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt,
 			      mifi_t mifi, int assert);
 static void mr6_netlink_event(struct mr_table *mrt, struct mfc6_cache *mfc,
 			      int cmd);
-static void mrt6msg_netlink_event(struct mr_table *mrt, struct sk_buff *pkt);
+static void mrt6msg_netlink_event(const struct mr_table *mrt, struct sk_buff *pkt);
 static int ip6mr_rtm_dumproute(struct sk_buff *skb,
 			       struct netlink_callback *cb);
 static void mroute_clean_tables(struct mr_table *mrt, int flags);
@@ -608,11 +608,12 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb,
 	if (ip6mr_fib_lookup(net, &fl6, &mrt) < 0)
 		goto tx_err;
 
-	read_lock(&mrt_lock);
 	dev->stats.tx_bytes += skb->len;
 	dev->stats.tx_packets++;
-	ip6mr_cache_report(mrt, skb, mrt->mroute_reg_vif_num, MRT6MSG_WHOLEPKT);
-	read_unlock(&mrt_lock);
+	rcu_read_lock();
+	ip6mr_cache_report(mrt, skb, READ_ONCE(mrt->mroute_reg_vif_num),
+			   MRT6MSG_WHOLEPKT);
+	rcu_read_unlock();
 	kfree_skb(skb);
 	return NETDEV_TX_OK;
 
@@ -718,8 +719,10 @@ static int mif6_delete(struct mr_table *mrt, int vifi, int notify,
 	RCU_INIT_POINTER(v->dev, NULL);
 
 #ifdef CONFIG_IPV6_PIMSM_V2
-	if (vifi == mrt->mroute_reg_vif_num)
-		mrt->mroute_reg_vif_num = -1;
+	if (vifi == mrt->mroute_reg_vif_num) {
+		/* Pairs with READ_ONCE() in ip6mr_cache_report() and reg_vif_xmit() */
+		WRITE_ONCE(mrt->mroute_reg_vif_num, -1);
+	}
 #endif
 
 	if (vifi + 1 == mrt->maxvif) {
@@ -922,7 +925,7 @@ static int mif6_add(struct net *net, struct mr_table *mrt,
 	netdev_tracker_alloc(dev, &v->dev_tracker, GFP_ATOMIC);
 #ifdef CONFIG_IPV6_PIMSM_V2
 	if (v->flags & MIFF_REGISTER)
-		mrt->mroute_reg_vif_num = vifi;
+		WRITE_ONCE(mrt->mroute_reg_vif_num, vifi);
 #endif
 	if (vifi + 1 > mrt->maxvif)
 		mrt->maxvif = vifi + 1;
@@ -1033,10 +1036,10 @@ static void ip6mr_cache_resolve(struct net *net, struct mr_table *mrt,
 /*
  *	Bounce a cache query up to pim6sd and netlink.
  *
- *	Called under mrt_lock.
+ *	Called under rcu_read_lock()
  */
 
-static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
+static int ip6mr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt,
 			      mifi_t mifi, int assert)
 {
 	struct sock *mroute6_sk;
@@ -1077,7 +1080,7 @@ static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
 		if (assert == MRT6MSG_WRMIFWHOLE)
 			msg->im6_mif = mifi;
 		else
-			msg->im6_mif = mrt->mroute_reg_vif_num;
+			msg->im6_mif = READ_ONCE(mrt->mroute_reg_vif_num);
 		msg->im6_pad = 0;
 		msg->im6_src = ipv6_hdr(pkt)->saddr;
 		msg->im6_dst = ipv6_hdr(pkt)->daddr;
@@ -1112,10 +1115,8 @@ static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
 	skb->ip_summed = CHECKSUM_UNNECESSARY;
 	}
 
-	rcu_read_lock();
 	mroute6_sk = rcu_dereference(mrt->mroute_sk);
 	if (!mroute6_sk) {
-		rcu_read_unlock();
 		kfree_skb(skb);
 		return -EINVAL;
 	}
@@ -1124,7 +1125,7 @@ static int ip6mr_cache_report(struct mr_table *mrt, struct sk_buff *pkt,
 
 	/* Deliver to user space multicast routing algorithms */
 	ret = sock_queue_rcv_skb(mroute6_sk, skb);
-	rcu_read_unlock();
+
 	if (ret < 0) {
 		net_warn_ratelimited("mroute6: pending queue full, dropping entries\n");
 		kfree_skb(skb);
@@ -2042,7 +2043,9 @@ static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 		vif->bytes_out += skb->len;
 		vif_dev->stats.tx_bytes += skb->len;
 		vif_dev->stats.tx_packets++;
+		rcu_read_lock();
 		ip6mr_cache_report(mrt, skb, vifi, MRT6MSG_WHOLEPKT);
+		rcu_read_unlock();
 		goto out_free;
 	}
 #endif
@@ -2155,10 +2158,12 @@ static void ip6_mr_forward(struct net *net, struct mr_table *mrt,
 			       c->_c.mfc_un.res.last_assert +
 			       MFC_ASSERT_THRESH)) {
 			c->_c.mfc_un.res.last_assert = jiffies;
+			rcu_read_lock();
 			ip6mr_cache_report(mrt, skb, true_vifi, MRT6MSG_WRONGMIF);
 			if (mrt->mroute_do_wrvifwhole)
 				ip6mr_cache_report(mrt, skb, true_vifi,
 						   MRT6MSG_WRMIFWHOLE);
+			rcu_read_unlock();
 		}
 		goto dont_forward;
 	}
@@ -2465,7 +2470,7 @@ static size_t mrt6msg_netlink_msgsize(size_t payloadlen)
 	return len;
 }
 
-static void mrt6msg_netlink_event(struct mr_table *mrt, struct sk_buff *pkt)
+static void mrt6msg_netlink_event(const struct mr_table *mrt, struct sk_buff *pkt)
 {
 	struct net *net = read_pnet(&mrt->net);
 	struct nlmsghdr *nlh;