Re: [RESEND,V2] drm: fsl-dcu: Fix no fb check bug

[Stefan Agner <stefan@agner.ch>]

On 2016-01-08 01:20, Emil Velikov wrote:
> Hi guys,
> 
> Am I loosing the plot here or something feels amiss here ?
> 
> On 6 January 2016 at 06:12, Meng Yi <meng.yi@nxp.com> wrote:
>> For state->fb or state->crtc may be NULL in fsl_dcu_drm_plane_atomic_check
>> function, if so, return 0.
>>
>> Signed-off-by: Meng Yi <meng.yi@nxp.com>
>> Signed-off-by: Jianwei Wang <jianwei.wang.chn@gmail.com>
>>
>> ---
>>
>> change in v2:
>> -Add state->crtc check
>> -return 0 when state->fb or state->crtc is NULL, instead of -EINVAL
>> Adviced by Daniel Stone
>>
>>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c
>> index 4b13cf9..8965580 100644
>> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c
>> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c
>> @@ -41,6 +41,9 @@ static int fsl_dcu_drm_plane_atomic_check(struct drm_plane *plane,
>>  {
>>         struct drm_framebuffer *fb = state->fb;
>>
>> +       if (!state->fb || !state->crtc)
>> +               return 0;
>> +
> Namely: if we return success here core drm will end up calling the
> atomic_update...
> 

After atomic_check atomic_disable could be called too. However, this
seem not directly depend on state'>fb, but more on plane->state->crtc.



>>         switch (fb->pixel_format) {
>>         case DRM_FORMAT_RGB565:
>>         case DRM_FORMAT_RGB888:
>> @@ -85,9 +88,6 @@ static void fsl_dcu_drm_plane_atomic_update(struct drm_plane *plane,
>>         unsigned int alpha, bpp;
>>         int index, ret;
>>
>> -       if (!fb)
>> -               return;
>> -
> ... which no longer has the !fb check, and we'll crash with null deref
> a few lines below ?


If there is a legitimate situation where fb is null which also
ultimately leads to a atomic_commit, I guess we should keep the return
here...

--
Stefan
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