netdev - RE: [PATCH net-next] net: thunderbolt: Clear finished Tx frame bus address in tbnet_tx

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Message-ID: <ac633155508e401bab2111ca5b0f8ba1@AcuMS.aculab.com>
Date:   Mon, 20 Nov 2017 14:46:53 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mika Westerberg' <mika.westerberg@...ux.intel.com>,
        David Miller <davem@...emloft.net>
CC:     "michael.jamet@...el.com" <michael.jamet@...el.com>,
        "yehezkel.bernat@...el.com" <yehezkel.bernat@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next] net: thunderbolt: Clear finished Tx frame bus
 address in tbnet_tx_callback()

From: Mika Westerberg
> Sent: 13 November 2017 10:22
> To: David Miller
> Cc: michael.jamet@...el.com; yehezkel.bernat@...el.com; netdev@...r.kernel.org
> Subject: Re: [PATCH net-next] net: thunderbolt: Clear finished Tx frame bus address in
> tbnet_tx_callback()
> 
> On Sat, Nov 11, 2017 at 07:21:24PM +0900, David Miller wrote:
> > From: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > Date: Thu,  9 Nov 2017 13:46:28 +0300
> >
> > > When Thunderbolt network interface is disabled or when the cable is
> > > unplugged the driver releases all allocated buffers by calling
> > > tbnet_free_buffers() for each ring. This function then calls
> > > dma_unmap_page() for each buffer it finds where bus address is non-zero.
> > > Now, we only clear this bus address when the Tx buffer is sent to the
> > > hardware so it is possible that the function finds an entry that has
> > > already been unmapped.
> > >
> > > Enabling DMA-API debugging catches this as well:
> > >
> > >   thunderbolt 0000:06:00.0: DMA-API: device driver tries to free DMA
> > >     memory it has not allocated [device address=0x0000000068321000] [size=4096 bytes]
> > >
> > > Fix this by clearing the bus address of a Tx frame right after we have
> > > unmapped the buffer.
> > >
> > > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> >
> > Applied, but assuming zero is a non-valid DMA address is never a good
> > idea.  That's why we have the DMA error code signaling abstracted.
> 
> There does not seem to be a way to mark DMA address invalid in a driver
> so we probably need to add a flag to struct tbnet_frame instead.

Can you use the length?

	David