[PATCHv2 net-next] net: use rcu_dereference_protected to fetch sk_dst_cache in sk_destruct

[Xin Long]

As Eric noticed, in .sk_destruct, sk->sk_dst_cache update is prevented, and
no barrier is needed for this. So change to use rcu_dereference_protected()
instead of rcu_dereference_check() to fetch sk_dst_cache in there.

v1->v2:
  - no change, repost after net-next is open.

Reported-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/decnet/af_decnet.c | 2 +-
 net/ipv4/af_inet.c     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/decnet/af_decnet.c b/net/decnet/af_decnet.c
index bdccc46..c1fa478 100644
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -444,7 +444,7 @@ static void dn_destruct(struct sock *sk)
        skb_queue_purge(&scp->other_xmit_queue);
        skb_queue_purge(&scp->other_receive_queue);
 
-       dst_release(rcu_dereference_check(sk->sk_dst_cache, 1));
+       dst_release(rcu_dereference_protected(sk->sk_dst_cache, 1));
 }
 
 static unsigned long dn_memory_pressure;
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index eab3ebd..375be06 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -156,7 +156,7 @@ void inet_sock_destruct(struct sock *sk)
        WARN_ON(sk->sk_forward_alloc);
 
        kfree(rcu_dereference_protected(inet->inet_opt, 1));
-       dst_release(rcu_dereference_check(sk->sk_dst_cache, 1));
+       dst_release(rcu_dereference_protected(sk->sk_dst_cache, 1));
        dst_release(sk->sk_rx_dst);
        sk_refcnt_debug_dec(sk);
 }
-- 
2.1.0