linux-kernel - Re: drivers/platform/surface/surface3-wmi.c:60:14: warning: variable 'status' set but not used

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Date:   Thu, 4 Feb 2021 16:10:57 +0100
From:   Maximilian Luz <luzmaximilian@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: drivers/platform/surface/surface3-wmi.c:60:14: warning: variable
 'status' set but not used



On 2/4/21 12:36 PM, Hans de Goede wrote:
> Hi,
> 
> On 1/4/21 4:24 PM, Maximilian Luz wrote:
>> On 1/4/21 3:52 PM, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 12/29/20 4:58 AM, kernel test robot wrote:
>>>> Hi Maximilian,
>>>>
>>>> FYI, the error/warning still remains.
>>>>
>>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>>>> head:   dea8dcf2a9fa8cc540136a6cd885c3beece16ec3
>>>> commit: f23027ca3d48b6f93c5994069fb25b73539fdf34 platform/surface: Move Surface 3 WMI driver to platform/surface
>>>> date:   9 weeks ago
>>>> config: x86_64-randconfig-r001-20201221 (attached as .config)
>>>> compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
>>>> reproduce (this is a W=1 build):
>>>>           # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f23027ca3d48b6f93c5994069fb25b73539fdf34
>>>>           git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>>>           git fetch --no-tags linus master
>>>>           git checkout f23027ca3d48b6f93c5994069fb25b73539fdf34
>>>>           # save the attached .config to linux build tree
>>>>           make W=1 ARCH=x86_64
>>>>
>>>> If you fix the issue, kindly add following tag as appropriate
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>>
>>>> All warnings (new ones prefixed by >>):
>>>>
>>>>      drivers/platform/surface/surface3-wmi.c: In function 's3_wmi_query_block':
>>>>>> drivers/platform/surface/surface3-wmi.c:60:14: warning: variable 'status' set but not used [-Wunused-but-set-variable]
>>>>         60 |  acpi_status status;
>>>>            |              ^~~~~~
>>>
>>> I guess fixing this would require something like this:
>>>
>>> From: Hans de Goede <hdegoede@...hat.com>
>>> Subject: [PATCH] platform/surface: surface3-wmi: Fix variable 'status' set but not used compiler warning
>>>
>>> Explictly check the status rather then relying on output.pointer staying
>>> NULL on an error. This silences the following compiler warning:
>>>
>>> drivers/platform/surface/surface3-wmi.c:60:14: warning: variable 'status' set but not used [-Wunused-but-set-variable]
>>>
>>> Reported-by: kernel test robot <lkp@...el.com>
>>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>>> ---
>>>    drivers/platform/surface/surface3-wmi.c | 4 ++++
>>>    1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/platform/surface/surface3-wmi.c b/drivers/platform/surface/surface3-wmi.c
>>> index 130b6f52a600..4b7f79c0b78e 100644
>>> --- a/drivers/platform/surface/surface3-wmi.c
>>> +++ b/drivers/platform/surface/surface3-wmi.c
>>> @@ -63,6 +63,10 @@ static int s3_wmi_query_block(const char *guid, int instance, int *ret)
>>>          mutex_lock(&s3_wmi_lock);
>>>        status = wmi_query_block(guid, instance, &output);
>>> +    if (ACPI_FAILURE(status)) {
>>> +        error = -EIO;
>>> +        goto out_free_unlock;
>>> +    }
>>>          obj = output.pointer;
>>>   
>>> Maximilian, can you review and/or test this fix please ?
>>
>> Ah, this was on my TODO list (among looking at some other things in this
>> driver), sorry that I haven't gotten to it yet. I'd have proposed pretty
>> much the exact same thing.
>>
>> One thing to note though: You should initialize obj with NULL. Keeping
>> it uninitialized may mess with kfree() under out_free_unlock.
>>
>> Unfortunately I don't have access to a Surface 3 to test, but apart from
>> not initializing obj, this patch looks good to me. You may add my
>> reviewed-by tag once you've fixed that.
> 
> Thank you, and sorry for being a bit slow with my follow up.

No worries.
  
> I've added the obj = NULL initialization and added your reviewed-by tag.
> 
> I'm sending this out as an official patch submission for the archives now
> and then I'll apply it to my review-hans branch right away, so no need
> for you to do anything :)
> 
>> Also note that drivers/platform/x86/msi-wmi.c suffers from the same
>> problem in msi_wmi_query_block() and should receive a similar fix.
> 
> Thanks, I'll prep a patch for that too.

Perfect, thanks!

Regards,
Max

> 
> Regards,
> 
> Hans
>