Re: [PATCH net-next] net: thunderbolt: Clear finished Tx frame bus address in tbnet_tx_callback()

[David Miller <davem@davemloft.net>]

From: Mika Westerberg <mika.westerberg@linux.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@linux.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.