Re: [PATCH] drm/nouveau/gsp: Fix possible NULL pointer dereference warning in r535_dmac_alloc

[Danilo Krummrich]

On Sat Apr 18, 2026 at 9:14 AM CEST, sunliming wrote:
> From: sunliming <sunliming@xxxxxxxxxx>
>
> Fix below smatch warnings:
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c:178 r535_dmac_alloc()
> warn: 'args' can also be NULL

Please write a commit description that explains also the underlying problem; see
more below.

> Signed-off-by: sunliming <sunliming@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c
> index 6e63df816d85..6dec2623d0be 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c
> @@ -172,6 +172,8 @@ r535_dmac_alloc(struct nvkm_disp *disp, u32 oclass, int inst, u32 put_offset,
>  
>  	args = nvkm_gsp_rm_alloc_get(&disp->rm.object, (oclass << 16) | inst, oclass,
>  				     sizeof(*args), dmac);
> +	if (!args)
> +		return -ENOMEM;

Are we sure that this can ever return NULL in the first place? I know that
nvkm_gsp_rm_alloc_get() internally checks for IS_ERR_OR_NULL(), but I couldn't
find anything within the callchain that would actually return NULL.

That said, I think IS_ERR_OR_NULL() checks are misleading.

>  	if (IS_ERR(args))
>  		return PTR_ERR(args);
>  
> -- 
> 2.25.1