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

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Date: Tue, 13 Feb 2024 17:57:59 +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 Tue, 13 Feb 2024 at 15:50, Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> 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>

After running this through CI:

Tested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org> #sc7180, sdm845

> >         DRM_MODESET_LOCK_ALL_END(dev, ctx, ret);
>
>
> --
> With best wishes
> Dmitry



-- 
With best wishes
Dmitry