2022-04-06 15:57:48

by Xiaomeng Tong

Subject: [PATCH v2] drm/gma500: fix a potential repeat execution in psb_driver_load

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 <[email protected]>
---

changes since v1:
- goto outside the loop (Xiaomeng Tong)

v1: https://lore.kernel.org/lkml/[email protected]/

---
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);

if (ret)
--
2.17.1

2022-04-12 20:40:55

by Patrik Jakobsson

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 <[email protected]> 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 <[email protected]>
> ---
>
> changes since v1:
> - goto outside the loop (Xiaomeng Tong)
>
> v1: https://lore.kernel.org/lkml/[email protected]/
>
> ---
> 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
>

2022-04-13 12:57:03

by Xiaomeng Tong

Subject: Re: [PATCH v2] drm/gma500: fix a potential repeat execution in psb_driver_load

On Tue, 12 Apr 2022 16:58:24 +0200, Patrik Jakobsson wrote:
> 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;
> }

Yes, it looks better.
I have sent a PATCH v3 with changes as you suggested, please check it.
Thank you very much.

--
Xiaomeng Tong