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

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Message-ID: <20161125002702.GA14085@electric-eye.fr.zoreil.com>
Date:   Fri, 25 Nov 2016 01:27:02 +0100
From:   Francois Romieu <romieu@...zoreil.com>
To:     Mark Lord <mlord@...ox.com>
Cc:     David Miller <davem@...emloft.net>, hayeswang@...ltek.com,
        netdev@...r.kernel.org, nic_swsd@...ltek.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH net 1/2] r8152: fix the sw rx checksum is unavailable

Mark Lord <mlord@...ox.com> :
[...]
> >From tracing through the powerpc arch code, this is the buffer that
> is being directly DMA'd into.  And the USB layer does an invalidate_dcache
> on that entire buffer before initiating the DMA (confirmed via printk).
> 
> The driver itself NEVER writes anything to that buffer,
> and nobody else has a pointer to it other than the USB host controller,
> so there's nothing else that can write to it either.
> 
> According to the driver writer, the chip should only ever write a fresh
> rx_desc struct at the beginning of a buffer, never ASCII data.
> 
> So how does that buffer end up containing ASCII data from the NFS transfers?

Through aliasing the URB was given a page that contains said (previously)
received file. The ethernet chip/usb host does not write anything in it.
There could be a device or a driver problem but it may not be the real
problem.

So far the analysis focused on "how was this corrupted content written into
this receive buffer page ?". If I read David correctly (?) the "nobody
else has a pointer to it other than the USB host controller" point may be
replaced with "the pointer to it aliases some already used page".

-- 
Ueimor