inet: Cleanup on charging memory for newly accepted sockets

If there is no net-memcg associated with the sock, don't bother
calculating its memory usage for charge.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Link: https://lore.kernel.org/r/20230620092712.16217-1-wuyun.abel@bytedance.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/inet_connection_sock.c

@@ -706,20 +706,23 @@ struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern)
 out:
 	release_sock(sk);
 	if (newsk && mem_cgroup_sockets_enabled) {
-		int amt;
+		int amt = 0;
 
 		/* atomically get the memory usage, set and charge the
 		 * newsk->sk_memcg.
 		 */
 		lock_sock(newsk);
 
-		/* The socket has not been accepted yet, no need to look at
-		 * newsk->sk_wmem_queued.
-		 */
-		amt = sk_mem_pages(newsk->sk_forward_alloc +
-				   atomic_read(&newsk->sk_rmem_alloc));
 		mem_cgroup_sk_alloc(newsk);
-		if (newsk->sk_memcg && amt)
+		if (newsk->sk_memcg) {
+			/* The socket has not been accepted yet, no need
+			 * to look at newsk->sk_wmem_queued.
+			 */
+			amt = sk_mem_pages(newsk->sk_forward_alloc +
+					   atomic_read(&newsk->sk_rmem_alloc));
+		}
+
+		if (amt)
 			mem_cgroup_charge_skmem(newsk->sk_memcg, amt,
 						GFP_KERNEL | __GFP_NOFAIL);