netdev - RE: [PATCH net 1/2] r8152: fix the sw rx checksum is unavailable

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Message-ID: <0835B3720019904CB8F7AA43166CEEB2010562B1@RTITMBSV03.realtek.com.tw>
Date:   Fri, 25 Nov 2016 06:31:18 +0000
From:   Hayes Wang <hayeswang@...ltek.com>
To:     Mark Lord <mlord@...ox.com>, David Miller <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        nic_swsd <nic_swsd@...ltek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: RE: [PATCH net 1/2] r8152: fix the sw rx checksum is unavailable

Mark Lord [mailto:mlord@...ox.com]
> Sent: Friday, November 25, 2016 12:44 AM
[...]
> The bad data in this case is ASCII:
> 
>          "SRC=m3400:/ TARGET=/m340"
> 
> This data is what is seen in /run/mount/utab, a file that is read/written over NFS on
> each boot.
> 
>          "SRC=m3400:/ TARGET=/m3400 ROOT=/
> ATTRS=nolock,addr=192.168.8.1\n"
> 
> But how does this ASCII data end up at offset zero of the rx buffer??
> Not possible -- this isn't even stale data, because only an rx_desc could
> be at that offset in that buffer.
> 
> So even if this were a platform memory coherency issue, one should still
> never see ASCII data at the beginning of an rx buffer.  The driver NEVER
> writes anything to the rx buffers.  Only the USB hardware ever does.
> 
> And only the r8152 dongle/driver exhibits this issue.
> Other USB dongles do not.  They *might* still have such issues,
> but because they use software checksums, the bad packets are caught/rejected.

Do you test it by rebooting? Maybe you could try a patch
commit 93fe9b183840 ("r8152: reset the bmu"). However, it should
only occur for the first urb buffer after rx is reset. I don't
think you would reset the rx frequently, so the situation seems
to be different.

Best Regards,
Hayes