netdev - Re: data corruption in skge hardware

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Date:	Mon, 7 Nov 2011 09:13:27 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org
Subject: Re: data corruption in skge hardware

On Mon, 7 Nov 2011 11:42:11 -0500 (EST)
Mikulas Patocka <mpatocka@...hat.com> wrote:

> Hi
> 
> I found a data corruption in skge network card.
> 
> The card is this: "03:06.0 Ethernet controller: 3Com Corporation 3c940 
> 10/100/1000Base-T [Marvell] (rev 10)"
> 
> The machine is two quad core Opterons with HT2000 north bridge and HT1000 
> south bridge.
> 
> When "scatter-gather" and "generic-segmentation-offload" are enabled, the 
> card sends out corrupted packets.
> 
> It normally manifests as a ssh connection drop once per few days, but I 
> found a workload that triggers this bug quickly.
> 
> I ran tcpdump on both sending and receiving machine and caught the packet 
> corruption:
> 
> correct packet (on the sending machine):
> 19:03:21.131836 IP hydra.ssh > phoebe.58913: Flags [P.], seq 53712:53808, 
> ack 1, win 193, options [nop,nop,TS val 8677173 ecr 1211608], length 96
>         0x0000:  4510 0094 c7bf 4000 4006 f12d c0a8 8007
>         0x0010:  c0a8 800e 0016 e621 2d64 84e6 1fc2 3f5b
>         0x0020:  8018 00c1 81ed 0000 0101 080a 0084 6735
>         0x0030:  0012 7cd8 4301 4af9 87c9 d2b4 8ba6 aedb
>         0x0040:  0572 1738 93db 789c 634b 4386 d013 db27
>         0x0050:  258b 6fa6 743c d429 a5e1 162f 2721 19bf
>         0x0060:  6669 a5c3 6bea 89ec a635 b8b4 8727 38c1
>         0x0070:  139f 5989 781b 49dd 79f5 4dfe 78ac ecb0
>         0x0080:  546c 33e0 0953 04bc 0647 a9d4 2fc4 cba0
>         0x0090:  44b2 3b01
> 
> incorrect packet (on the receiving machine):
> 19:03:21.133174 IP hydra.ssh > phoebe.58913: Flags [P.], seq 53712:53808, 
> ack 1, win 193, options [nop,nop,TS val 8677173 ecr 1211608], length 96
>         0x0000:  4510 0094 c7bf 4000 4006 f12d c0a8 8007
>         0x0010:  c0a8 800e 0016 e621 2d64 84e6 1fc2 3f5b
>         0x0020:  8018 00c1 6aa4 0000 0101 080a 0084 6735
>         0x0030:  0012 7cd8 0000 0000 0000 0000 0010 0000
>         0x0040:  0000 0000 0000 0000 0000 0000 0000 0000
>         0x0050:  0000 0000 0000 0000 0000 00c0 dc92 4702
>         0x0060:  88ff ff00 0000 0000 0000 0000 0000 0000
>         0x0070:  0000 0000 0000 0000 0000 0000 0000 0000
>         0x0080:  0000 0000 0000 0000 0000 0000 0000 0000
>         0x0090:  0000 00e0
> 
> Obviously, scatter-gather doesn't work, the header is correct, but the 
> packet body was likely read from random memory.
> 
> I tried to use "clflush" instruction on the transmit descriptor and the 
> packet body to test if it is a cache-coherency issue, but the corruption 
> was still there.
> 
> I tried to limit memory to 2G to test if it was a problem with high 
> memory, but the corruption was still there.
> 
> I tries olded kernels (as far as 2.6.34), the corruption was still there, 
> but it took much more time to trigger it with old kernels.
> 
> 
> Do you have other reports of data corruption with skge hardware? Shouldn't 
> the driver set "scatter-gather" off by default because it is unreliable?

No reports, of problems.
Scatter-gather is used all the time by normal TCP connections.
I suspect something different because of the IOMMU and separate sockets.

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