linux-kernel - Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver

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Date:	Mon, 16 Mar 2009 14:50:46 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Atsushi Nemoto <anemo@....ocn.ne.jp>
Cc:	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"haavard.skinnemoen@...el.com" <haavard.skinnemoen@...el.com>
Subject: Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver

On Fri, 2009-03-13 at 07:16 -0700, Atsushi Nemoto wrote:
> On Fri, 13 Mar 2009 01:19:50 +0900 (JST), Atsushi Nemoto <anemo@....ocn.ne.jp> wrote:
> > Subject: dmaengine: Use chan_id provided by DMA device driver
> > From: Atsushi Nemoto <anemo@....ocn.ne.jp>
> > 
> > If chan_id was already given by the DMA device driver, use it.
> > Otherwise assign an incremental number for each channels.
> > 
> > This allows the DMA device driver to reserve some channel ID numbers.
> ...
> > @@ -663,7 +664,9 @@ int dma_async_device_register(struct dma_device *device)
> >  			continue;
> >  		}
> >  
> > -		chan->chan_id = chancnt++;
> > +		if (!chan->chan_id)
> > +			chan->chan_id = chan_id++;
> > +		chancnt++;
> >  		chan->dev->device.class = &dma_devclass;
> >  		chan->dev->device.parent = device->dev;
> >  		chan->dev->chan = chan;
> 
> This patch will fix another potential problem.  Some driver, for
> example ipu, assumes chan_id is an index of its internal array.  But
> dmaengine core does not guarantee it.
> 
> 	/* represent channels in sysfs. Probably want devs too */
> 	list_for_each_entry(chan, &device->channels, device_node) {
> 		chan->local = alloc_percpu(typeof(*chan->local));
> 		if (chan->local == NULL)
> 			continue;
> 		chan->dev = kzalloc(sizeof(*chan->dev), GFP_KERNEL);
> 		if (chan->dev == NULL) {
> 			free_percpu(chan->local);
> 			continue;
> 		}
> 
> 		chan->chan_id = chancnt++;
> 		...
> 	}
> 	device->chancnt = chancnt;
> 
> If alloc_percpu or kzalloc failed, chan_id does not match with its
> position in device->channels list.
> 
> 
> And above "continue" looks buggy anyway.  Keeping incomplete channels
> in device->channels list looks very dangerous...

Yes it does.  Here is the proposed fix:
----->
dmaengine: fail device registration if channel registration fails

From: Dan Williams <dan.j.williams@...el.com>

Atsushi points out:
"If alloc_percpu or kzalloc failed, chan_id does not match with its
position in device->channels list.

And above "continue" looks buggy anyway.  Keeping incomplete channels
in device->channels list looks very dangerous..."

Reported-by: Atsushi Nemoto <anemo@....ocn.ne.jp>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/dma/dmaengine.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index a589930..fa14e8b 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -652,13 +652,15 @@ int dma_async_device_register(struct dma_device *device)
 
 	/* represent channels in sysfs. Probably want devs too */
 	list_for_each_entry(chan, &device->channels, device_node) {
+		rc = -ENOMEM;
 		chan->local = alloc_percpu(typeof(*chan->local));
 		if (chan->local == NULL)
-			continue;
+			goto err_out;
 		chan->dev = kzalloc(sizeof(*chan->dev), GFP_KERNEL);
 		if (chan->dev == NULL) {
 			free_percpu(chan->local);
-			continue;
+			chan->local = NULL;
+			goto err_out;
 		}
 
 		chan->chan_id = chancnt++;
@@ -675,6 +677,8 @@ int dma_async_device_register(struct dma_device *device)
 		if (rc) {
 			free_percpu(chan->local);
 			chan->local = NULL;
+			kfree(chan->dev);
+			atomic_dec(idr_ref);
 			goto err_out;
 		}
 		chan->client_count = 0;


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