linux-kernel - Re: [PATCH v2] drm/gma500: fix a potential repeat execution in psb_driver

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Message-ID: <CAMeQTsaXM-ddGLukxuEJvm+0UtuJEZGL_5KEY8h9ZPH-ZxmBsQ@mail.gmail.com>
Date:   Tue, 12 Apr 2022 16:58:24 +0200
From:   Patrik Jakobsson <patrik.r.jakobsson@...il.com>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/gma500: fix a potential repeat execution in psb_driver_load

On Wed, Apr 6, 2022 at 1:31 PM Xiaomeng Tong <xiam0nd.tong@...il.com> wrote:
>
> Instead of exiting the loop as expected when an entry is found, the
> list_for_each_entry() continues until the traversal is complete. To
> avoid potential executing 'ret = gma_backlight_init(dev);' repeatly,
> goto outside the loop when the entry is found.
>
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> ---
>
> changes since v1:
>  - goto outside the loop (Xiaomeng Tong)
>
> v1: https://lore.kernel.org/lkml/20220401115811.9656-1-xiam0nd.tong@gmail.com/
>
> ---
>  drivers/gpu/drm/gma500/psb_drv.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/gma500/psb_drv.c b/drivers/gpu/drm/gma500/psb_drv.c
> index 2aff54d505e2..929fd47548b4 100644
> --- a/drivers/gpu/drm/gma500/psb_drv.c
> +++ b/drivers/gpu/drm/gma500/psb_drv.c
> @@ -400,9 +400,10 @@ static int psb_driver_load(struct drm_device *dev, unsigned long flags)
>                 case INTEL_OUTPUT_LVDS:
>                 case INTEL_OUTPUT_MIPI:
>                         ret = gma_backlight_init(dev);
> -                       break;
> +                       goto out;
>                 }
>         }
> +out:
>         drm_connector_list_iter_end(&conn_iter);

Hi,
This would work but using gotos like this easily turns the code into
spaghetti. See "7. Centralized exiting of functions" in
Documentation/process/coding-style.rst for when to use gotos.

In this particular case I think we are better off using an
if-statement. What about something like this:

if (gma_encoder->type == INTEL_OUTPUT_LVDS ||
    gma_encoder->type == INTEL_OUTPUT_MIPI) {
        ret = gma_backlight_init();
        break;
}

-Patrik

>
>         if (ret)
> --
> 2.17.1
>