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

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Date:   Wed, 20 Jan 2021 15:55:33 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Daniel Vetter <daniel@...ll.ch>
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



Le mer. 20 janv. 2021 à 15:04, Daniel Vetter <daniel@...ll.ch> a 
écrit :
> 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

Alright, I will add a wrapper.

Cheers,
-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