RE: [kbuild] drivers/usb/gadget/udc/fsl_udc_core.c:1055 fsl_ep_fifo_status() error: we previously assumed '_ep->desc' could be null (see line 1055)

From: Ran Wang <ran.wang_1@nxp.com>
To: Dan Carpenter <dan.carpenter@oracle.com>,
	"kbuild@lists.01.org" <kbuild@lists.01.org>
Cc: "lkp@intel.com" <lkp@intel.com>,
	"kbuild-all@lists.01.org" <kbuild-all@lists.01.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	Peter Chen <peter.chen@nxp.com>
Subject: RE: [kbuild] drivers/usb/gadget/udc/fsl_udc_core.c:1055 fsl_ep_fifo_status() error: we previously assumed '_ep->desc' could be null (see line 1055)
Date: Tue, 23 Jun 2020 02:22:18 +0000	[thread overview]
Message-ID: <AM6PR04MB54138B87957CFB06EC9DF351F1940@AM6PR04MB5413.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20200622182023.GX4282@kadam>

Hi Dan

On Tuesday, June 23, 2020 2:20 AM, Dan Carpenter wrote:

<snip>

> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> 
> New smatch warnings:
> drivers/usb/gadget/udc/fsl_udc_core.c:1055 fsl_ep_fifo_status() error: we
> previously assumed '_ep->desc' could be null (see line 1055)
> 

<snip>

> 
> 2ea6698d7b9266 drivers/usb/gadget/fsl_udc_core.c     Anatolij Gustschin
> 2011-04-18  1047  static int fsl_ep_fifo_status(struct usb_ep *_ep)
> 2ea6698d7b9266 drivers/usb/gadget/fsl_udc_core.c     Anatolij Gustschin
> 2011-04-18  1048  {
> 2ea6698d7b9266 drivers/usb/gadget/fsl_udc_core.c     Anatolij Gustschin
> 2011-04-18  1049  	struct fsl_ep *ep;
> 2ea6698d7b9266 drivers/usb/gadget/fsl_udc_core.c     Anatolij Gustschin
> 2011-04-18  1050  	struct fsl_udc *udc;
> 2ea6698d7b9266 drivers/usb/gadget/fsl_udc_core.c     Anatolij Gustschin
> 2011-04-18  1051  	int size = 0;
> 2ea6698d7b9266 drivers/usb/gadget/fsl_udc_core.c     Anatolij Gustschin
> 2011-04-18  1052  	u32 bitmask;
> 6414e94c203d92 drivers/usb/gadget/fsl_udc_core.c     Li Yang
> 2011-11-23  1053  	struct ep_queue_head *qh;
> 2ea6698d7b9266 drivers/usb/gadget/fsl_udc_core.c     Anatolij Gustschin
> 2011-04-18  1054
> 75eaa498c99eeb drivers/usb/gadget/udc/fsl_udc_core.c Nikhil Badola
> 2019-10-21 @1055  	if (!_ep || _ep->desc || !(_ep->desc->bEndpointAddress&0xF))
>                                          ^^^^^^^^^ Reversed NULL test.  This will always return -ENODEV.  (Or possibly crash.  But I suspect it always returns -ENODEV instead of crashing).

So the kernel test reports warning in case of '_ep->desc is null', right? 

My understanding is that this judgement would return -ENODEV when
executing '... || _ep-desc ||..' and never execute '_ep->desc->bEndpointAddress' part,
so crash would not happen, am I right?

> The container_of() macro doesn't dereference anything, btw.  It just does
> pointer math.  I think it would be cleaner to use ep_index() like the original
> code did.  In other words, perhaps it would look best written like this:

Yes, I agree using ep_index() would be easier for reading, just feel a little bit
uncomfortable to mix checking on _ep and it's container (ep) in the same line.

> 	ep = container_of(_ep, struct fsl_ep, ep);
> 	if (!_ep || !_ep->desc || ep_index(ep) == 0)
> 
> 

BTW, Nikhil Badola has left NXP (Freesale), so his email address is invalid now.

Thanks & Regards,
Ran