re: NTB: Use unique DMA channels for TX and RX

re: NTB: Use unique DMA channels for TX and RX

[Dan Carpenter]

Hello Dave Jiang,

This is a semi-automatic email about new static checker warnings.

The patch 569410ca756c: "NTB: Use unique DMA channels for TX and RX" 
from Jul 13, 2015, leads to the following Smatch complaint:

drivers/ntb/ntb_transport.c:2008 ntb_transport_max_size()
	 error: we previously assumed 'qp->tx_dma_chan' could be null (see line 2005)

drivers/ntb/ntb_transport.c
  2004	
  2005		if (!qp->tx_dma_chan && !qp->rx_dma_chan)

Patch adds new checks for NULL.  Was || intended here perhaps?

  2006			return qp->tx_max_frame - sizeof(struct ntb_payload_header);
  2007	
  2008		copy_align = max(qp->tx_dma_chan->device->copy_align,
  2009				 qp->rx_dma_chan->device->copy_align);

Patch adds unchecked dereferences.

  2010	

regards,
dan carpenter

RE: NTB: Use unique DMA channels for TX and RX

[Allen Hubbe]

From: linux-ntb@googlegroups.com On Behalf Of Dan Carpenter
> Subject: re: NTB: Use unique DMA channels for TX and RX
> 
> drivers/ntb/ntb_transport.c:2008 ntb_transport_max_size()
> 	 error: we previously assumed 'qp->tx_dma_chan' could be null (see
> line 2005)
> 
> drivers/ntb/ntb_transport.c
>   2004
>   2005		if (!qp->tx_dma_chan && !qp->rx_dma_chan)

I seem to recall commenting on this in patch v1:

>> -	if (!qp->dma_chan)
>> +	if (!qp->tx_dma_chan && !qp->rx_dma_chan)
>
> Unusual to see "if (not && not)" in code, but it looks correct in this case.
>
> if (no dma at all)
>	return without any alignment restriction;
>
> Is that right?

Maybe I was wrong to say "looks correct" because this static checker warning sure looks real.

> 
> Patch adds new checks for NULL.  Was || intended here perhaps?
> 
>   2006			return qp->tx_max_frame - sizeof(struct
> ntb_payload_header);
>   2007
>   2008		copy_align = max(qp->tx_dma_chan->device->copy_align,
>   2009				 qp->rx_dma_chan->device->copy_align);

I think this is the part that actually needs to be fixed.  Maybe this whole function should be:

copy_align = max(dma_copy_align(qp->tx_dma_chan),
                 dma_copy_align(qp->rx_dma_chan));

where dma_copy_align is:

if (!chan)
        return 1;
return chan->device->copy_align;

> 
> Patch adds unchecked dereferences.
> 
>   2010
>