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 12:36:56 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Maximilian Luz <luzmaximilian@...il.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

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.

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.

Regards,

Hans