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

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Date:   Mon, 4 Jan 2021 16:24:54 +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 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.

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.

Regards,
Max