linux-kernel - Re: [PATCH v2 2/3] drm/ingenic: Register devm action to cleanup encoders

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Date:   Wed, 20 Jan 2021 15:04:59 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     David Airlie <airlied@...ux.ie>, Sam Ravnborg <sam@...nborg.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        od@...c.me, dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] drm/ingenic: Register devm action to cleanup encoders

On Wed, Jan 20, 2021 at 2:21 PM Paul Cercueil <paul@...pouillou.net> wrote:
>
>
>
> Le mer. 20 janv. 2021 à 14:01, Daniel Vetter <daniel@...ll.ch> a
> écrit :
> > On Wed, Jan 20, 2021 at 1:36 PM Paul Cercueil <paul@...pouillou.net>
> > wrote:
> >>
> >>  Since the encoders have been devm-allocated, they will be freed way
> >>  before drm_mode_config_cleanup() is called. To avoid use-after-free
> >>  conditions, we then must ensure that drm_encoder_cleanup() is called
> >>  before the encoders are freed.
> >>
> >>  v2: Use the new __drmm_simple_encoder_alloc() function
> >>
> >>  Fixes: c369cb27c267 ("drm/ingenic: Support multiple panels/bridges")
> >>  Cc: <stable@...r.kernel.org> # 5.8+
> >>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> >>  ---
> >>
> >>  Notes:
> >>      Use the V1 of this patch to fix v5.11 and older kernels. This
> >> V2 only
> >>      applies on the current drm-misc-next branch.
> >>
> >>   drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 16 +++++++---------
> >>   1 file changed, 7 insertions(+), 9 deletions(-)
> >>
> >>  diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> >> b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> >>  index 7bb31fbee29d..158433b4c084 100644
> >>  --- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> >>  +++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> >>  @@ -1014,20 +1014,18 @@ static int ingenic_drm_bind(struct device
> >> *dev, bool has_components)
> >>                          bridge =
> >> devm_drm_panel_bridge_add_typed(dev, panel,
> >>
> >> DRM_MODE_CONNECTOR_DPI);
> >>
> >>  -               encoder = devm_kzalloc(dev, sizeof(*encoder),
> >> GFP_KERNEL);
> >>  -               if (!encoder)
> >>  -                       return -ENOMEM;
> >>  +               encoder = __drmm_simple_encoder_alloc(drm,
> >> sizeof(*encoder), 0,
> >
> > Please don't use the __ prefixed functions, those are the internal
> > ones. The official one comes with type checking and all that included.
> > Otherwise lgtm.
> > -Daniel
>
> The non-prefixed one assumes that I want to allocate a struct that
> contains the encoder, not just the drm_encoder itself.

Hm, but using the internal one is also a bit too ugly. A
drm_plain_simple_enocder_alloc(drm, type) wrapper would be the right
thing here I think? Setting the offsets and struct sizes directly in
these in drivers really doesn't feel like a good idea. I think simple
encoder is the only case where we really have a need for a
non-embeddable struct.
-Daniel

>
> -Paul
>
> >>  +
> >> DRM_MODE_ENCODER_DPI);
> >>  +               if (IS_ERR(encoder)) {
> >>  +                       ret = PTR_ERR(encoder);
> >>  +                       dev_err(dev, "Failed to init encoder:
> >> %d\n", ret);
> >>  +                       return ret;
> >>  +               }
> >>
> >>                  encoder->possible_crtcs = 1;
> >>
> >>                  drm_encoder_helper_add(encoder,
> >> &ingenic_drm_encoder_helper_funcs);
> >>
> >>  -               ret = drm_simple_encoder_init(drm, encoder,
> >> DRM_MODE_ENCODER_DPI);
> >>  -               if (ret) {
> >>  -                       dev_err(dev, "Failed to init encoder:
> >> %d\n", ret);
> >>  -                       return ret;
> >>  -               }
> >>  -
> >>                  ret = drm_bridge_attach(encoder, bridge, NULL, 0);
> >>                  if (ret) {
> >>                          dev_err(dev, "Unable to attach bridge\n");
> >>  --
> >>  2.29.2
> >>
> >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
>
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch