netdev - Re: [PATCH 2/2] benet: fix the misusage of zero dma address

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Message-Id: <20100405163942P.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 5 Apr 2010 16:40:18 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	sathyap@...verengines.com
Cc:	fujita.tomonori@....ntt.co.jp, subbus@...verengines.com,
	sarveshwarb@...verengines.com, ajitk@...verengines.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] benet: fix the misusage of zero dma address

On Mon, 5 Apr 2010 12:40:59 +0530
Sathya Perla <sathyap@...verengines.com> wrote:

> Hi Fujita, thanks for the patch; pls see below:
> 
> On 02/04/10 11:53 +0900, FUJITA Tomonori wrote:
> > benet driver wrongly assumes that zero is an invalid dma address
> > (calls dma_unmap_page for only non zero dma addresses). Zero is a
> > valid dma address on some architectures. The dma length can be used
> > here.
> > 
> > Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > ---
> >  drivers/net/benet/be_main.c |    6 ++++--
> >  1 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/benet/be_main.c b/drivers/net/benet/be_main.c
> > index 8d5e27b..8828c7d 100644
> > --- a/drivers/net/benet/be_main.c
> > +++ b/drivers/net/benet/be_main.c
> > @@ -394,13 +394,15 @@ static void unmap_tx_frag(struct pci_dev *pdev, struct be_eth_wrb *wrb,
> >  	be_dws_le_to_cpu(wrb, sizeof(*wrb));
> >  
> >  	dma = (u64)wrb->frag_pa_hi << 32 | (u64)wrb->frag_pa_lo;
> > -	if (dma != 0) {
> > +	if (wrb->frag_len) {
> >  		if (unmap_single)
> >  			pci_unmap_single(pdev, dma, wrb->frag_len,
> >  				PCI_DMA_TODEVICE);
> >  		else
> >  			pci_unmap_page(pdev, dma, wrb->frag_len,
> >  				PCI_DMA_TODEVICE);
> > +
> > +		wrb->frag_len = 0;
> Why does wrb->frag_len need to be reset here?
> In the TX path, it is set to the proper value for data wrbs and zero
> for dummy and hdr wrbs.

I guess that I misunderstood why unmap_tx_frag() checks a dma address.
The checking is necessary to avoid calling pci_unamp_* API for dummy
hdr wrbs?

Anyway, if wrb->frag_len doesn't need to be reset here, the following
patch is ok?

=
From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: [PATCH v2 2/2] benet: fix the misusage of zero dma address

benet driver wrongly assumes that zero is an invalid dma address
(calls dma_unmap_page for only non zero dma addresses). Zero is a
valid dma address on some architectures. The dma length can be used
here.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
---
 drivers/net/benet/be_main.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/net/benet/be_main.c b/drivers/net/benet/be_main.c
index a27a0a1..c95e1a2 100644
--- a/drivers/net/benet/be_main.c
+++ b/drivers/net/benet/be_main.c
@@ -404,7 +404,7 @@ static void unmap_tx_frag(struct pci_dev *pdev, struct be_eth_wrb *wrb,
 	be_dws_le_to_cpu(wrb, sizeof(*wrb));
 
 	dma = (u64)wrb->frag_pa_hi << 32 | (u64)wrb->frag_pa_lo;
-	if (dma != 0) {
+	if (wrb->frag_len) {
 		if (unmap_single)
 			pci_unmap_single(pdev, dma, wrb->frag_len,
 				PCI_DMA_TODEVICE);
-- 
1.7.0


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