lkml.org 
[lkml]   [2001]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: 2.4.4: Kernel crash, possibly tcp related
On Tue, May 01, 2001 at 08:44:52PM +0400, kuznet@ms2.inr.ac.ru wrote:
> 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...

I understsand the explanation but I don't think my patch is wrong, I
think it's simpler and faster instead.

My argument is very simple, if send_head points to skb and skb->len is
zero and we are running in such slow path, it is obvious the send_head
_was_ NULL when we entered the critical section, so it's perfectly fine
to set send_head back to null and to unlink the skb as the only actions
to undo the skb_entail. That's all. I don't see how my patch can fail.
If I'm missing something I'd love a further explanation indeed. Thanks!

>
> 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);


Andrea
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:52    [W:0.069 / U:0.128 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site