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

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Message-ID: <06e868cb-f96e-46af-9484-a613de0baaaf@kadam.mountain>
Date:   Thu, 26 Oct 2023 12:04:00 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Su Hui <suhui@...china.com>
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 Thu, Oct 26, 2023 at 04:46:29PM +0800, Su Hui wrote:
> 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.

Yeah.  It's super useful for kernel development.  It helps to understand
how functions are called and where variables are set etc.  The smatch
documentation is crap, I know.  But I did write a short blog about the
cross function DB.

https://staticthinking.wordpress.com/2023/05/02/the-cross-function-db/

It's simple to build, but it takes a long time.  Just run
smatch_scripts/build_kernel_data.sh

regards,
dan carpenter