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Re: Help on a network driver ... [strange TCP problems]

To: David Brownell <david-b@xxxxxxxxxxx>
Subject: Re: Help on a network driver ... [strange TCP problems]
From: Andi Kleen <ak@xxxxxx>
Date: Fri, 9 Feb 2001 02:33:50 +0100
Cc: Rabeeh Khoury <rabeeh@xxxxxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <054701c09212$0806bda0$6800000a@xxxxxxxxxxxx>; from david-b@xxxxxxxxxxx on Thu, Feb 08, 2001 at 10:12:14PM +0100
References: <059f01c09083$82ed9e20$6800000a@xxxxxxxxxxxx> <3A811B95.4080303@xxxxxxxxxxxxx> <054701c09212$0806bda0$6800000a@xxxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx
On Thu, Feb 08, 2001 at 10:12:14PM +0100, David Brownell wrote:
> I just got a report of a symptom, likely related, where
> tcpdump shows the ACK is getting sent and then dropped.
> (Below, it's not even getting sent.)  And in fact, I just saw
> this version a few moments ago myself.

This usually points to checksum problems. tcpdump doesn't check checksums.

> 
> I've seen this problem with this driver off and on since
> about test8; it might have been there in test6/test7 when
> the driver was first developed (it's still "experimental")
> without being noticed ("intermittent"), but in any case
> this is rather perplexing.  What do folk do when trying
> to get TCP to tell them what's up?  Enabling TCP_DEBUG
> or NETDEBUG is no help at all.

Add printks or ktrace calls until you get enlighted.

You could e.g. instrument __kfree_skb to see where it is freed
(using __builtin_return_address(0) when you're using the right compiler)

-Andi

-- 
This is like TV. I don't like TV.

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