netdev - [PATCH net-next] tipc: tipc_udp_recv() cleanup vs rcu verbs

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Date:   Tue, 23 Apr 2019 09:24:46 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jon Maloy <jon.maloy@...csson.com>,
        Ying Xue <ying.xue@...driver.com>
Subject: [PATCH net-next] tipc: tipc_udp_recv() cleanup vs rcu verbs

First thing tipc_udp_recv() does is to use rcu_dereference_sk_user_data(),
and this is really hinting we already own rcu_read_lock() from the caller
(UDP stack).

No need to add another rcu_read_lock()/rcu_read_unlock() pair.

Also use rcu_dereference() instead of rcu_dereference_rtnl()
in the data path.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Jon Maloy <jon.maloy@...csson.com>
Cc: Ying Xue <ying.xue@...driver.com>
---
 net/tipc/udp_media.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
index 6f166fbbfff148b7d3774ece0d68203d9925b3da..7413cbc9b638af492d6a592df957a3229fa6a3fa 100644
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -354,10 +354,9 @@ static int tipc_udp_recv(struct sock *sk, struct sk_buff *skb)
 	skb_pull(skb, sizeof(struct udphdr));
 	hdr = buf_msg(skb);
 
-	rcu_read_lock();
-	b = rcu_dereference_rtnl(ub->bearer);
+	b = rcu_dereference(ub->bearer);
 	if (!b)
-		goto rcu_out;
+		goto out;
 
 	if (b && test_bit(0, &b->up)) {
 		tipc_rcv(sock_net(sk), skb, b);
@@ -368,11 +367,9 @@ static int tipc_udp_recv(struct sock *sk, struct sk_buff *skb)
 	if (unlikely(msg_user(hdr) == LINK_CONFIG)) {
 		err = tipc_udp_rcast_disc(b, skb);
 		if (err)
-			goto rcu_out;
+			goto out;
 	}
 
-rcu_out:
-	rcu_read_unlock();
 out:
 	kfree_skb(skb);
 	return 0;
-- 
2.21.0.593.g511ec345e18-goog