net: prepare (struct ubuf_info)->refcnt conversion

In order to convert this atomic_t refcnt to refcount_t,
we need to init the refcount to one to not trigger
a 0 -> 1 transition.

This also removes one atomic operation in fast path.

v2: removed dead code in sock_zerocopy_put_abort()
as suggested by Willem.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -963,7 +963,7 @@ struct ubuf_info *sock_zerocopy_alloc(struct sock *sk, size_t size)
 	uarg->len = 1;
 	uarg->bytelen = size;
 	uarg->zerocopy = 1;
-	atomic_set(&uarg->refcnt, 0);
+	atomic_set(&uarg->refcnt, 1);
 	sock_hold(sk);
 
 	return uarg;
@@ -1005,6 +1005,7 @@ struct ubuf_info *sock_zerocopy_realloc(struct sock *sk, size_t size,
 			uarg->len++;
 			uarg->bytelen = bytelen;
 			atomic_set(&sk->sk_zckey, ++next);
+			sock_zerocopy_get(uarg);
 			return uarg;
 		}
 	}
@@ -1102,13 +1103,6 @@ void sock_zerocopy_put_abort(struct ubuf_info *uarg)
 		atomic_dec(&sk->sk_zckey);
 		uarg->len--;
 
-		/* sock_zerocopy_put expects a ref. Most sockets take one per
-		 * skb, which is zero on abort. tcp_sendmsg holds one extra, to
-		 * avoid an skb send inside the main loop triggering uarg free.
-		 */
-		if (sk->sk_type != SOCK_STREAM)
-			atomic_inc(&uarg->refcnt);
-
 		sock_zerocopy_put(uarg);
 	}
 }

net/ipv4/tcp.c

@@ -1190,8 +1190,6 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 			goto out_err;
 		}
 
-		/* skb may be freed in main loop, keep extra ref on uarg */
-		sock_zerocopy_get(uarg);
 		if (!(sk_check_csum_caps(sk) && sk->sk_route_caps & NETIF_F_SG))
 			uarg->zerocopy = 0;
 	}