linux-kernel - Re: [char-misc:char-misc-linus 3/3] drivers/misc/cardreader/rtsx_usb.c:639:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is true

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Message-ID: <1c13496a-9e45-38b6-1563-c09d412cf576@linuxfoundation.org>
Date:   Fri, 1 Jul 2022 09:52:57 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
        kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [char-misc:char-misc-linus 3/3]
 drivers/misc/cardreader/rtsx_usb.c:639:6: warning: variable 'ret' is used
 uninitialized whenever 'if' condition is true

On 7/1/22 9:39 AM, Nathan Chancellor wrote:
> On Fri, Jul 01, 2022 at 08:48:11AM -0600, Shuah Khan wrote:
>> On 7/1/22 2:59 AM, Greg Kroah-Hartman wrote:
>>> On Fri, Jul 01, 2022 at 04:49:50PM +0800, kernel test robot wrote:
>>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git char-misc-linus
>>>> head:   3776c78559853fd151be7c41e369fd076fb679d5
>>>> commit: 3776c78559853fd151be7c41e369fd076fb679d5 [3/3] misc: rtsx_usb: use separate command and response buffers
>>>> config: arm-buildonly-randconfig-r006-20220629 (https://download.01.org/0day-ci/archive/20220701/202207011658.rHJFVLWA-lkp@intel.com/config)
>>>> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project a9119143a2d1f4d0d0bc1fe0d819e5351b4e0deb)
>>>> reproduce (this is a W=1 build):
>>>>           wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>>>>           chmod +x ~/bin/make.cross
>>>>           # install arm cross compiling tool for clang build
>>>>           # apt-get install binutils-arm-linux-gnueabi
>>>>           # https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/commit/?id=3776c78559853fd151be7c41e369fd076fb679d5
>>>>           git remote add char-misc https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
>>>>           git fetch --no-tags char-misc char-misc-linus
>>>>           git checkout 3776c78559853fd151be7c41e369fd076fb679d5
>>>>           # save the config file
>>>>           mkdir build_dir && cp config build_dir/.config
>>>>           COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash drivers/misc/cardreader/
>>>>
>>>> If you fix the issue, kindly add following tag where applicable
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>>
>>>> All warnings (new ones prefixed by >>):
>>>>
>>>>>> drivers/misc/cardreader/rtsx_usb.c:639:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
>>>>              if (!ucr->rsp_buf)
>>>>                  ^~~~~~~~~~~~~
>>>>      drivers/misc/cardreader/rtsx_usb.c:678:9: note: uninitialized use occurs here
>>>>              return ret;
>>>>                     ^~~
>>>>      drivers/misc/cardreader/rtsx_usb.c:639:2: note: remove the 'if' if its condition is always false
>>>>              if (!ucr->rsp_buf)
>>>>              ^~~~~~~~~~~~~~~~~~
>>>>      drivers/misc/cardreader/rtsx_usb.c:622:9: note: initialize the variable 'ret' to silence this warning
>>>>              int ret;
>>>>                     ^
>>>>                      = 0
>>>>      1 warning generated.
>>>
>>> Odd, gcc doesn't show this for me.  Shuah, can you send a follow-on
>>> patch to fix this?  The warning does look correct.
>>>
>>
>> gcc didn't complain when I compiled either. I will send a follow-on patch.
> 
> Unfortunately, GCC won't warn for most uninitialized variables by
> default after 5.7, which included commit 78a5255ffb6a ("Stop the ad-hoc
> games with -Wno-maybe-initialized"). They will potentially show up at
> W=2 or with an explicit KCFLAGS=-Wmaybe-uninitialized (it does in this
> case):
> 

Thank you.

> | drivers/misc/cardreader/rtsx_usb.c: In function ‘rtsx_usb_probe’:
> | drivers/misc/cardreader/rtsx_usb.c:678:16: error: ‘ret’ may be used uninitialized [-Werror=maybe-uninitialized]
> |   678 |         return ret;
> |       |                ^~~
> | drivers/misc/cardreader/rtsx_usb.c:622:13: note: ‘ret’ was declared here
> |   622 |         int ret;
> |       |             ^~~
> | cc1: all warnings being treated as errors
> 

This is a bug and a good find. ret should have been set
in the if (!ucr->rsp_buf) before going to error handling.

I wonder if it would have been flagged if ret were to be
initialized to 0. Something to experiment.

thanks,
-- Shuah