Re: 2.4.4: Kernel crash, possibly tcp related

[kuznet@ms2.inr.ac.ru]

Hello!

> this is the strict fix:

Andrea, you caught the problem!

The fix is not right though (it is equivalent to straight
tp->send_head=NULL, as you noticed. It also corrupts queue in
an opposite manner.) Right fix is appended.

Explanation: in do_fault we must undo effect of enqueueing new segment
in the case the segment remained empty. tp->send_head points to
the first unsent skb in queue and it is NULL when and only when
all the skbs are already sent. (Invariant is: tp->send_head==NULL ||
tp->send_head->seq == tp->snd_nxt)
I crapped this case except for the case when queue is completely empty,
so that the last sent skb was accounted in packets_out twice...

Damn, what a silly mistake was it... shame.

Alexey


--- ../vger3-010426/linux/net/ipv4/tcp.c	Wed Apr 25 21:02:18 2001
+++ linux/net/ipv4/tcp.c	Tue May  1 20:38:44 2001
@@ -1185,7 +1187,7 @@
 	if (skb->len==0) {
 		if (tp->send_head == skb) {
 			tp->send_head = skb->prev;
-			if (tp->send_head == (struct sk_buff*)&sk->write_queue)
+			if (TCP_SKB_CB(skb)->seq == tp->snd_nxt)
 				tp->send_head = NULL;
 		}
 		__skb_unlink(skb, skb->list);