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Re: 2.6.9-rc1-mm5: TCP oopses

To: James Morris <jmorris@xxxxxxxxxx>
Subject: Re: 2.6.9-rc1-mm5: TCP oopses
From: "David S. Miller" <davem@xxxxxxxxxxxxx>
Date: Mon, 13 Sep 2004 19:08:58 -0700
Cc: akpm@xxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <Xine.LNX.4.44.0409132019170.22477-200000@thoron.boston.redhat.com>
References: <20040913015003.5406abae.akpm@osdl.org> <Xine.LNX.4.44.0409132019170.22477-200000@thoron.boston.redhat.com>
Sender: netdev-bounce@xxxxxxxxxxx
On Mon, 13 Sep 2004 20:25:38 -0400 (EDT)
James Morris <jmorris@xxxxxxxxxx> wrote:

> I'm experiencing TCP related oopses with this kernel (not seen in -mm4), 
> .config file attached.
> 
> Here are two backtraces, the first happened a few seconds after logging 
> in via ssh, the second happened soon after boot (using selinux=0, just to 
> make sure).

I think I fixed this one yesterday.  Callers of tcp_fragment()
in tcp_output.c were not accounting packets correctly.  I
believe this is what will fix it, and this is in Linus's
tree already.

I guess you have an e1000 in this box? :)
(either that or some other card whose driver
enables TSO by default)

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
#   2004/09/10 15:21:43-07:00 davem@xxxxxxxxxxxxxxxxxx 
#   [TCP]: Fix packet counting when fragmenting already sent packets.
#   
#   Calls to tcp_fragment() change the tso_factor of
#   an SKB, so we need to deal with that.
#   
#   Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
# 
# net/ipv4/tcp_output.c
#   2004/09/10 15:21:13-07:00 davem@xxxxxxxxxxxxxxxxxx +12 -2
#   [TCP]: Fix packet counting when fragmenting already sent packets.
#   
#   Calls to tcp_fragment() change the tso_factor of
#   an SKB, so we need to deal with that.
#   
#   Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
# 
diff -Nru a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
--- a/net/ipv4/tcp_output.c     2004-09-13 18:51:38 -07:00
+++ b/net/ipv4/tcp_output.c     2004-09-13 18:51:38 -07:00
@@ -681,8 +681,12 @@
                        TCP_SKB_CB(skb)->when = tcp_time_stamp;
                        if (tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC)))
                                break;
-                       /* Advance the send_head.  This one is sent out. */
+
+                       /* Advance the send_head.  This one is sent out.
+                        * This call will increment packets_out.
+                        */
                        update_send_head(sk, tp, skb);
+
                        tcp_minshall_update(tp, mss_now, skb);
                        sent_pkts = 1;
                }
@@ -968,11 +972,17 @@
                return -EAGAIN;
 
        if (skb->len > cur_mss) {
+               int old_factor = TCP_SKB_CB(skb)->tso_factor;
+               int new_factor;
+
                if (tcp_fragment(sk, skb, cur_mss))
                        return -ENOMEM; /* We'll try again later. */
 
                /* New SKB created, account for it. */
-               tcp_inc_pcount(&tp->packets_out, skb);
+               new_factor = TCP_SKB_CB(skb)->tso_factor;
+               tcp_dec_pcount_explicit(&tp->packets_out,
+                                       new_factor - old_factor);
+               tcp_inc_pcount(&tp->packets_out, skb->next);
        }
 
        /* Collapse two adjacent packets if worthwhile and we can. */

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