re: dmaengine: add interface of dma_get_slave_channel

re: dmaengine: add interface of dma_get_slave_channel

[Dan Carpenter]

Hello Zhangfei Gao,

The patch 7bb587f4eef8: "dmaengine: add interface of 
dma_get_slave_channel" from Jun 28, 2013, leads to the following 
warning: "drivers/dma/dmaengine.c:531 dma_get_slave_channel()
	 	error: potential NULL dereference 'chan'."

drivers/dma/dmaengine.c
   516  struct dma_chan *dma_get_slave_channel(struct dma_chan *chan)
   517  {
   518          int err = -EBUSY;
   519  
   520          /* lock against __dma_request_channel */
   521          mutex_lock(&dma_list_mutex);
   522  
   523          if (chan->client_count = 0)
   524                  err = dma_chan_get(chan);
   525          else
   526                  chan = NULL;
                        ^^^^^^^^^^^
   527  
   528          mutex_unlock(&dma_list_mutex);
   529  
   530          if (err)
   531                  pr_debug("%s: failed to get %s: (%d)\n",
   532                          __func__, dma_chan_name(chan), err);
                                                        ^^^^

Dereferenced here.

   533  
   534          return chan;

regards,
dan carpenter

Re: dmaengine: add interface of dma_get_slave_channel

[zhangfei]

On 13-08-15 03:51 AM, Dan Carpenter wrote:
> Hello Zhangfei Gao,
>
> The patch 7bb587f4eef8: "dmaengine: add interface of
> dma_get_slave_channel" from Jun 28, 2013, leads to the following
> warning: "drivers/dma/dmaengine.c:531 dma_get_slave_channel()
> 	 	error: potential NULL dereference 'chan'."
>
> drivers/dma/dmaengine.c
>     516  struct dma_chan *dma_get_slave_channel(struct dma_chan *chan)
>     517  {
>     518          int err = -EBUSY;
>     519
>     520          /* lock against __dma_request_channel */
>     521          mutex_lock(&dma_list_mutex);
>     522
>     523          if (chan->client_count = 0)
>     524                  err = dma_chan_get(chan);
>     525          else
>     526                  chan = NULL;
>                          ^^^^^^^^^^^
>     527
>     528          mutex_unlock(&dma_list_mutex);
>     529
>     530          if (err)
>     531                  pr_debug("%s: failed to get %s: (%d)\n",
>     532                          __func__, dma_chan_name(chan), err);
>                                                          ^^^^
>
> Dereferenced here.
>
>     533
>     534          return chan;
>
> regards,
> dan carpenter
>

Thanks Dan for point out.

I am sorry, make does not report such error here, is it config related.

Dear Vinod

Could I update this patch and resend to you?
Change to:
struct dma_chan *dma_get_slave_channel(struct dma_chan *chan)
{
         int err = -EBUSY;

         /* lock against __dma_request_channel */
         mutex_lock(&dma_list_mutex);

         if (chan->client_count = 0) {
                 err = dma_chan_get(chan);
                 if (err)
                         pr_debug("%s: failed to get %s: (%d)\n",
                                 __func__, dma_chan_name(chan), err);
         } else
                 chan = NULL;

         mutex_unlock(&dma_list_mutex);

         return chan;
}

Sorry for inconvenience.

Thanks