netdev - Re: Bug in drivers/net/ethernet/freescale/fec

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Message-ID: <1426254527.4173.98.camel@decadent.org.uk>
Date:	Fri, 13 Mar 2015 13:48:47 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Панов Андрей <rockford@...dex.ru>
Cc:	Nimrod Andy <b38611@...escale.com>, netdev@...r.kernel.org
Subject: Re: Bug in drivers/net/ethernet/freescale/fec_main.c, TX is broken.
 In 4.0.0-rc3

On Mon, 2015-03-09 at 22:50 +0300, Панов Андрей wrote:
> Hello!
> 
> Commit 2b995f63987013bacde99168218f9c7b252bdcf1 in 4.0.0-rc3 introduces a nasty bug in transmit, corrupting packets.
> 
> To reproduce:
> 
> $ dd if=/dev/zero of=zeros bs=1M count=20
> $ md5sum -b zeros
> 8f4e33f3dc3e414ff94e5fb6905cba8c *zeros
> 
> This checksum is correct.
> 
> Copy file "zeros" to another host with NFS, and it gets corrupted, checksum is changed.
> File should be big, small amounts of transmit isn't affected.
> 
> I use an i.MX6 Quad board.
> 
> If this commit is reverted, all works fine.

And the bug described in the commit message doesn't seem to exist in the
previous version.  The change just doesn't make sense to me.

I seem to remember DMA debug checks sometimes causing false positives
for network I/O, too.

Ben.

-- 
Ben Hutchings
Any smoothly functioning technology is indistinguishable from a rigged demo.

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