Re: [PATCH] dmaengine: Add a null pointer check to the dma_request_chan

[Kunwu Chan]

Thanks for your reply.

On 2024/1/22 19:25, Vinod Koul wrote:
> On 18-01-24, 11:30, Kunwu Chan wrote:
> > kasprintf() returns a pointer to dynamically allocated memory
> > which can be NULL upon failure. Ensure the allocation was successful
> > by checking the pointer validity.
> >
> > Signed-off-by: Kunwu Chan <chentao@xxxxxxxxxx>
> > ---
> >   drivers/dma/dmaengine.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > index 491b22240221..a6f808d13aa4 100644
> > --- a/drivers/dma/dmaengine.c
> > +++ b/drivers/dma/dmaengine.c
> > @@ -856,6 +856,8 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> >   #ifdef CONFIG_DEBUG_FS
> >   	chan->dbg_client_name = kasprintf(GFP_KERNEL, "%s:%s", dev_name(dev),
> >   					  name);
> > +	if (!chan->dbg_client_name)
> > +		return chan;
>
> That is wrong, you cant return a half done channel here
> Pls see rest of the code for reference
I handle the error path like line 862 in 'dma_request_chan', though i 
think it's not so perfect. Why it just return chan in line 862 when in 
error? I would be very grateful if it could help me solve this puzzle

dma_request_chan find and return the ``name`` DMA channel associated 
with the 'dev' device. The association is done via DT, ACPI or board 
file based dma_slave_map matching table.

So when error occurs, just do the opposite, like in 'dma_release_channel'.

look likes:
---

        chan->dbg_client_name = kasprintf(GFP_KERNEL, "%s:%s", 
dev_name(dev),
                                          name);
+       if (!chan->dbg_client_name) {
+               dma_cap_clear(DMA_SLAVE, chan->device->cap_mask);
+               dma_cap_zero(chan->device->cap_mask);
+               dma_chan_put(chan);
+               chan->slave = NULL;
+               chan = NULL;
+               return chan;
+       }

---
It's that right by clear the cap and set chan to NULL？


> >   #endif
> >   
> >   	chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
> > --
> > 2.39.2
--
Thanks,
  Kunwu