tcp: provide more information on the tcp receive_queue bugs

The addition of rcv_nxt allows to discern whether the skb
was out of place or tp->copied. Also catch fancy combination
of flags if necessary (sadly we might miss the actual causer
flags as it might have already returned).

Btw, we perhaps would want to forward copied_seq in
somewhere or otherwise we might have some nice loop with
WARN stuff within but where to do that safely I don't
know at this stage until more is known (but it is not
made significantly worse by this patch).
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -1183,7 +1183,9 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied)
 #if TCP_DEBUG
 	struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
 
-	WARN_ON(skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq));
+	WARN(skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq),
+	     KERN_INFO "cleanup rbuf bug: copied %X seq %X rcvnxt %X\n",
+	     tp->copied_seq, TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt);
 #endif
 
 	if (inet_csk_ack_scheduled(sk)) {
@@ -1430,11 +1432,13 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 			/* Now that we have two receive queues this
 			 * shouldn't happen.
 			 */
-			if (before(*seq, TCP_SKB_CB(skb)->seq)) {
-				printk(KERN_INFO "recvmsg bug: copied %X "
-				       "seq %X\n", *seq, TCP_SKB_CB(skb)->seq);
+			if (WARN(before(*seq, TCP_SKB_CB(skb)->seq),
+			     KERN_INFO "recvmsg bug: copied %X "
+				       "seq %X rcvnxt %X fl %X\n", *seq,
+				       TCP_SKB_CB(skb)->seq, tp->rcv_nxt,
+				       flags))
 				break;
-			}
+
 			offset = *seq - TCP_SKB_CB(skb)->seq;
 			if (tcp_hdr(skb)->syn)
 				offset--;
@@ -1443,8 +1447,9 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 			if (tcp_hdr(skb)->fin)
 				goto found_fin_ok;
 			WARN(!(flags & MSG_PEEK), KERN_INFO "recvmsg bug 2: "
-					"copied %X seq %X\n", *seq,
-					TCP_SKB_CB(skb)->seq);
+					"copied %X seq %X rcvnxt %X fl %X\n",
+					*seq, TCP_SKB_CB(skb)->seq,
+					tp->rcv_nxt, flags);
 		}
 
 		/* Well, if we have backlog, try to process it now yet. */