linux-kernel - Re: [PATCH] drm/msm/mdp5: check the return of kzalloc()

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Date:   Wed, 6 Apr 2022 09:24:22 -0700
From:   Rob Clark <robdclark@...il.com>
To:     xkernel.wang@...mail.com
Cc:     Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/mdp5: check the return of kzalloc()

On Thu, Mar 24, 2022 at 1:37 AM <xkernel.wang@...mail.com> wrote:
>
> From: Xiaoke Wang <xkernel.wang@...mail.com>
>
> kzalloc() is a memory allocation function which can return NULL when
> some internal memory errors happen. So it is better to check it to
> prevent potential wrong memory access.
>
> Signed-off-by: Xiaoke Wang <xkernel.wang@...mail.com>
> ---
>  drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> index c6b69af..5f914cc 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> @@ -90,15 +90,18 @@ static void mdp5_plane_reset(struct drm_plane *plane)
>                 __drm_atomic_helper_plane_destroy_state(plane->state);
>
>         kfree(to_mdp5_plane_state(plane->state));
> -       mdp5_state = kzalloc(sizeof(*mdp5_state), GFP_KERNEL);
> +       plane->state = NULL;

At this point, you could just:

    if (!mdp5_state)
       return;

BR,
-R

>
> -       if (plane->type == DRM_PLANE_TYPE_PRIMARY)
> -               mdp5_state->base.zpos = STAGE_BASE;
> -       else
> -               mdp5_state->base.zpos = STAGE0 + drm_plane_index(plane);
> -       mdp5_state->base.normalized_zpos = mdp5_state->base.zpos;
> +       mdp5_state = kzalloc(sizeof(*mdp5_state), GFP_KERNEL);
> +       if (mdp5_state) {
> +               if (plane->type == DRM_PLANE_TYPE_PRIMARY)
> +                       mdp5_state->base.zpos = STAGE_BASE;
> +               else
> +                       mdp5_state->base.zpos = STAGE0 + drm_plane_index(plane);
> +               mdp5_state->base.normalized_zpos = mdp5_state->base.zpos;
>
> -       __drm_atomic_helper_plane_reset(plane, &mdp5_state->base);
> +               __drm_atomic_helper_plane_reset(plane, &mdp5_state->base);
> +       }
>  }
>
>  static struct drm_plane_state *
> --