linux-kernel - Re: [PATCH] drm/crtc: fix uninitialized variable use even harder

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Date: Tue, 13 Feb 2024 15:50:38 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org, Rob Clark <robdclark@...omium.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Jani Nikula <jani.nikula@...el.com>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/crtc: fix uninitialized variable use even harder

On Mon, 12 Feb 2024 at 23:55, Rob Clark <robdclark@...il.com> wrote:
>
> From: Rob Clark <robdclark@...omium.org>
>
> DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
> which means we can't rely too much on variable initializers.
>
> Fixes: 6e455f5dcdd1 ("drm/crtc: fix uninitialized variable use")
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
> I have mixed feelings about DRM_MODESET_LOCK_ALL_BEGIN() (and friends)
> magic.  On one hand it simplifies the deadlock/back dance.  OTOH it
> conceals a nasty sharp edge.  Maybe it is better to have the complicated
> restart path a bit more explicit, like it was originally.
>
>  drivers/gpu/drm/drm_crtc.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index cb90e70d85e8..65f9f66933bb 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -904,6 +904,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
>         connector_set = NULL;
>         fb = NULL;
>         mode = NULL;
> +       num_connectors = 0;

Nit: I think we should move all this next to the
DRM_MODESET_LOCK_ALL_BEGIN() and drop initialisation from the prologue
of the function, but it's definitely a separate and more intrusive
story.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

>         DRM_MODESET_LOCK_ALL_END(dev, ctx, ret);


-- 
With best wishes
Dmitry