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

[sunliming@linux.dev]

2026年4月18日 20:12, "Danilo Krummrich" <dakr@kernel.org mailto:dakr@kernel.org?to=%22Danilo%20Krummrich%22%20%3Cdakr%40kernel.org%3E > 写到:


> 
> On Sat Apr 18, 2026 at 9:14 AM CEST, sunliming wrote:
> 
> > 
> > From: sunliming <sunliming@kylinos.cn>
> > 
> >  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@kylinos.cn>
> >  ---
> >  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.
> 
I also believe that the nvkm_gsp_rm_alloc_get function will not return NULL. My patch 
was merely intended to suppress a compiler warning and to guard against possible future 
changes in the implementation of nvkm_gsp_rm_alloc_get. Of course, the patch may be 
unnecessary, and I will defer to the maintainers' review conclusion.

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