linux-kernel - Re: [PATCH] vga_switcheroo: Fix impossible judgment condition

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Date:   Thu, 26 Oct 2023 16:46:29 +0800
From:   Su Hui <suhui@...china.com>
To:     Dan Carpenter <dan.carpenter@...aro.org>
Cc:     lukas@...ner.de, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
        daniel@...ll.ch, tiwai@...e.de, Jim.Qu@....com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] vga_switcheroo: Fix impossible judgment condition

On 2023/10/26 12:44, Dan Carpenter wrote:
> On Thu, Oct 26, 2023 at 10:10:57AM +0800, Su Hui wrote:
>> 'id' is enum type like unsigned int, so it will never be less than zero.
>>
>> Fixes: 4aaf448fa975 ("vga_switcheroo: set audio client id according to bound GPU id")
>> Signed-off-by: Su Hui <suhui@...china.com>
>> ---
>>   drivers/gpu/vga/vga_switcheroo.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
>> index 365e6ddbe90f..d3064466fd3a 100644
>> --- a/drivers/gpu/vga/vga_switcheroo.c
>> +++ b/drivers/gpu/vga/vga_switcheroo.c
>> @@ -375,7 +375,7 @@ int vga_switcheroo_register_audio_client(struct pci_dev *pdev,
>>   	mutex_lock(&vgasr_mutex);
>>   	if (vgasr_priv.active) {
>>   		id = vgasr_priv.handler->get_client_id(vga_dev);
>> -		if (id < 0) {
>> +		if ((int)id < 0) {
> Hi,
>
> I feel like you're using Smatch?  Which is great!  Fantastic!
Yep, Smatch helps me  a lot to find these bugs! I really like this 
excellent tool!
>
> Have you built the cross function database?  If you have there is a
> command that's useful.
Not yet, bu I want to build this.
> $ ~/smatch/smatch_db/smdb.py functions vga_switcheroo_handler get_client_id | tee where
> drivers/gpu/drm/nouveau/nouveau_acpi.c | (struct vga_switcheroo_handler)->get_client_id | nouveau_dsm_get_client_id | 1
> drivers/gpu/drm/amd/amdgpu/amdgpu_atpx_handler.c | (struct vga_switcheroo_handler)->get_client_id | amdgpu_atpx_get_client_id | 1
> drivers/gpu/drm/radeon/radeon_atpx_handler.c | (struct vga_switcheroo_handler)->get_client_id | radeon_atpx_get_client_id | 1
> drivers/platform/x86/apple-gmux.c | (struct vga_switcheroo_handler)->get_client_id | gmux_get_client_id | 1
> $ make cscope
> $ vim where
> Use cscope to jump to each of those four functions.  Move the cursor to
> the nouveau_dsm_get_client_id and hit CTRL-].
Sounds great! I must try this!
>
> They never return negatives.  The enum vga_switcheroo_client_id has a
> VGA_SWITCHEROO_UNKNOWN_ID define which I guess these functions are
> supposed to return on error.  They never do return that, but I bet
> that's what we are supposed to check for.  It honestly might be good
> to check for both...
>
> 		if ((int)id < 0 || id == VGA_SWITCHEROO_UNKNOWN_ID) {
> 			mutex_unlock(&vgasr_mutex);
> 			return -EINVAL;
> 		}
Agreed, I will send v2 patch soon.
Really thanks for your wonderful suggestion! :)

Su Hui

> regards,
> dan carpenter
>