linux-kernel - Re: [kbuild] drivers/usb/gadget/udc/fsl_udc_core.c:1055 fsl_ep_fifo_status() error: we previously assumed '

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Message-ID: <20200623103651.GZ4282@kadam>
Date:   Tue, 23 Jun 2020 13:36:51 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Ran Wang <ran.wang_1@....com>
Cc:     "kbuild@...ts.01.org" <kbuild@...ts.01.org>,
        "lkp@...el.com" <lkp@...el.com>,
        "kbuild-all@...ts.01.org" <kbuild-all@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Peter Chen <peter.chen@....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)

On Tue, Jun 23, 2020 at 02:22:18AM +0000, Ran Wang wrote:
> 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@...el.com>
> > Reported-by: Dan Carpenter <dan.carpenter@...cle.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?

Yeah.  I can't imagine how _ep->desc is NULL.  It gets set to non-NULL
in fsl_ep_enable() and then set to NULL in fsl_ep_disable().

regards,
dan carpenter