[v3,3/5] drm/msm: fix fb references in async update

Submitted by Helen Koike on March 14, 2019, 12:20 a.m.

Details

Message ID 20190314002027.7833-4-helen.koike@collabora.com
State New
Headers show
Series "drm: Fix fb changes for async updates" ( rev: 3 ) in DRI devel

Commit Message

Helen Koike March 14, 2019, 12:20 a.m.
Async update callbacks are expected to set the old_fb in the new_state
so prepare/cleanup framebuffers are balanced.

Cc: <stable@vger.kernel.org> # v4.14+
Fixes: 224a4c970987 ("drm/msm: update cursors asynchronously through atomic")
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Helen Koike <helen.koike@collabora.com>

---
Hello,

As mentioned in the cover letter,
But I couldn't test on MSM because I don't have the hardware and I would
appreciate if anyone could test it.

In other platforms (VC4, AMD, Rockchip), there is a hidden
drm_framebuffer_get(new_fb)/drm_framebuffer_put(old_fb) in async_update
that is wrong, but I couldn't identify those here, not sure if it is hidden
somewhere else, but if tests fail this is probably the cause.

Thanks!
Helen

Changes in v3: None
Changes in v2:
- update CC stable and Fixes tag

 drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 4 ++++
 1 file changed, 4 insertions(+)

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
index be13140967b4..b854f471e9e5 100644
--- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
+++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
@@ -502,6 +502,8 @@  static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
 static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
 					   struct drm_plane_state *new_state)
 {
+	struct drm_framebuffer *old_fb = plane->state->fb;
+
 	plane->state->src_x = new_state->src_x;
 	plane->state->src_y = new_state->src_y;
 	plane->state->crtc_x = new_state->crtc_x;
@@ -524,6 +526,8 @@  static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
 
 	*to_mdp5_plane_state(plane->state) =
 		*to_mdp5_plane_state(new_state);
+
+	new_state->fb = old_fb;
 }
 
 static const struct drm_plane_helper_funcs mdp5_plane_helper_funcs = {

Comments

On Wed, Mar 13, 2019 at 8:21 PM Helen Koike <helen.koike@collabora.com> wrote:
>
> Async update callbacks are expected to set the old_fb in the new_state
> so prepare/cleanup framebuffers are balanced.
>
> Cc: <stable@vger.kernel.org> # v4.14+
> Fixes: 224a4c970987 ("drm/msm: update cursors asynchronously through atomic")
> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Helen Koike <helen.koike@collabora.com>
>
> ---
> Hello,
>
> As mentioned in the cover letter,
> But I couldn't test on MSM because I don't have the hardware and I would
> appreciate if anyone could test it.
>
> In other platforms (VC4, AMD, Rockchip), there is a hidden
> drm_framebuffer_get(new_fb)/drm_framebuffer_put(old_fb) in async_update
> that is wrong, but I couldn't identify those here, not sure if it is hidden
> somewhere else, but if tests fail this is probably the cause.
>
> Thanks!
> Helen

Apologies, I haven't had a chance to test this yet, and it is likely
to be a few weeks before I have a chance..

That said, not refcnt'ing the fb seems suspicious.   I read the
explanation in the other patches, but kind of think it is more clear
to keep the extra refcnt'ing.. or at least have a comment.

I do a bit wonder if we hold the ref to the outgoing cursor long
enough.. I think the hw will actually continue to scan it out until
the next vblank.  But Archit was the one who added async_update
support so maybe that is handled somewhere else.  It's been a while
since I've looked at this.

BR,
-R



>
> Changes in v3: None
> Changes in v2:
> - update CC stable and Fixes tag
>
>  drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> index be13140967b4..b854f471e9e5 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> @@ -502,6 +502,8 @@ static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
>  static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
>                                            struct drm_plane_state *new_state)
>  {
> +       struct drm_framebuffer *old_fb = plane->state->fb;
> +
>         plane->state->src_x = new_state->src_x;
>         plane->state->src_y = new_state->src_y;
>         plane->state->crtc_x = new_state->crtc_x;
> @@ -524,6 +526,8 @@ static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
>
>         *to_mdp5_plane_state(plane->state) =
>                 *to_mdp5_plane_state(new_state);
> +
> +       new_state->fb = old_fb;
>  }
>
>  static const struct drm_plane_helper_funcs mdp5_plane_helper_funcs = {
> --
> 2.20.1
>
Hi Rob,

On 3/27/19 11:52 AM, Rob Clark wrote:
> On Wed, Mar 13, 2019 at 8:21 PM Helen Koike <helen.koike@collabora.com> wrote:
>>
>> Async update callbacks are expected to set the old_fb in the new_state
>> so prepare/cleanup framebuffers are balanced.
>>
>> Cc: <stable@vger.kernel.org> # v4.14+
>> Fixes: 224a4c970987 ("drm/msm: update cursors asynchronously through atomic")
>> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
>> Signed-off-by: Helen Koike <helen.koike@collabora.com>
>>
>> ---
>> Hello,
>>
>> As mentioned in the cover letter,
>> But I couldn't test on MSM because I don't have the hardware and I would
>> appreciate if anyone could test it.
>>
>> In other platforms (VC4, AMD, Rockchip), there is a hidden
>> drm_framebuffer_get(new_fb)/drm_framebuffer_put(old_fb) in async_update
>> that is wrong, but I couldn't identify those here, not sure if it is hidden
>> somewhere else, but if tests fail this is probably the cause.
>>
>> Thanks!
>> Helen
> 
> Apologies, I haven't had a chance to test this yet, and it is likely
> to be a few weeks before I have a chance..
> 
> That said, not refcnt'ing the fb seems suspicious.   I read the
> explanation in the other patches, but kind of think it is more clear
> to keep the extra refcnt'ing.. or at least have a comment.


Refcnt'ing is taken care by drm_mode_cursor_universal() when calling
drm_atomic_helper_update_plane().
The other codes had a drm_atomic_set_fb_for_plane() (which get a
referent of the new fb and put the old fb), but the problem is that the
cleanup_plane will also put the ref of the old fb.
In the other drivers I saw, drm_atomic_set_fb_for_plane() shouldn't be
called, but this issue should be triggered very easily with a test.

I can add this is in the async_check() docs.

> 
> I do a bit wonder if we hold the ref to the outgoing cursor long
> enough.. I think the hw will actually continue to scan it out until
> the next vblank.  But Archit was the one who added async_update
> support so maybe that is handled somewhere else.  It's been a while
> since I've looked at this.

I don't know much about MSM, but if I understand correctly, MSM don't
support true async, is that correct?

Then I think we need to do something similar to the rockchip:

https://patchwork.kernel.org/patch/10852039/

and setup a drm_flip_work_queue().
But this seems another problem that is already there no? Not really
related to this patch. I could send a separate patch for this (but I
don't have the means to test it).

Regards,
Helen

> 
> BR,
> -R
> 
> 
> 
>>
>> Changes in v3: None
>> Changes in v2:
>> - update CC stable and Fixes tag
>>
>>  drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
>> index be13140967b4..b854f471e9e5 100644
>> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
>> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
>> @@ -502,6 +502,8 @@ static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
>>  static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
>>                                            struct drm_plane_state *new_state)
>>  {
>> +       struct drm_framebuffer *old_fb = plane->state->fb;
>> +
>>         plane->state->src_x = new_state->src_x;
>>         plane->state->src_y = new_state->src_y;
>>         plane->state->crtc_x = new_state->crtc_x;
>> @@ -524,6 +526,8 @@ static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
>>
>>         *to_mdp5_plane_state(plane->state) =
>>                 *to_mdp5_plane_state(new_state);
>> +
>> +       new_state->fb = old_fb;
>>  }
>>
>>  static const struct drm_plane_helper_funcs mdp5_plane_helper_funcs = {
>> --
>> 2.20.1
>>
>
Hello,

On 3/13/19 9:20 PM, Helen Koike wrote:
> Async update callbacks are expected to set the old_fb in the new_state
> so prepare/cleanup framebuffers are balanced.
> 
> Cc: <stable@vger.kernel.org> # v4.14+
> Fixes: 224a4c970987 ("drm/msm: update cursors asynchronously through atomic")
> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Helen Koike <helen.koike@collabora.com>
> 
> ---
> Hello,
> 
> As mentioned in the cover letter,
> But I couldn't test on MSM because I don't have the hardware and I would
> appreciate if anyone could test it.

I got this tested on a dragonboard 410c, no regressions where found and
no extra warnings.

These two tests where already failing for other reasons:
flip-vs-cursor-crc-atomic
flip-vs-cursor-crc-legacy

If you want to see the full log:

https://people.collabora.com/~koike/drm-fixes-results.zip

Thanks
Helen

> 
> In other platforms (VC4, AMD, Rockchip), there is a hidden
> drm_framebuffer_get(new_fb)/drm_framebuffer_put(old_fb) in async_update
> that is wrong, but I couldn't identify those here, not sure if it is hidden
> somewhere else, but if tests fail this is probably the cause.
> 
> Thanks!
> Helen
> 
> Changes in v3: None
> Changes in v2:
> - update CC stable and Fixes tag
> 
>  drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> index be13140967b4..b854f471e9e5 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> @@ -502,6 +502,8 @@ static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
>  static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
>  					   struct drm_plane_state *new_state)
>  {
> +	struct drm_framebuffer *old_fb = plane->state->fb;
> +
>  	plane->state->src_x = new_state->src_x;
>  	plane->state->src_y = new_state->src_y;
>  	plane->state->crtc_x = new_state->crtc_x;
> @@ -524,6 +526,8 @@ static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
>  
>  	*to_mdp5_plane_state(plane->state) =
>  		*to_mdp5_plane_state(new_state);
> +
> +	new_state->fb = old_fb;
>  }
>  
>  static const struct drm_plane_helper_funcs mdp5_plane_helper_funcs = {
>
On Fri, May 31, 2019 at 10:54 AM Helen Koike <helen@koikeco.de> wrote:
>
> Hello,
>
> On 3/13/19 9:20 PM, Helen Koike wrote:
> > Async update callbacks are expected to set the old_fb in the new_state
> > so prepare/cleanup framebuffers are balanced.
> >
> > Cc: <stable@vger.kernel.org> # v4.14+
> > Fixes: 224a4c970987 ("drm/msm: update cursors asynchronously through atomic")
> > Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Signed-off-by: Helen Koike <helen.koike@collabora.com>

Thanks, I'm not super happy about the refcnt'ing subtleness here
(mostly because it makes it harder to page in how things work on
kernel/display side after spending most of my time in userspace/mesa),
but I don't want to hold this up..

Acked-by: Rob Clark <robdclark@gmail.com>

> >
> > ---
> > Hello,
> >
> > As mentioned in the cover letter,
> > But I couldn't test on MSM because I don't have the hardware and I would
> > appreciate if anyone could test it.
>
> I got this tested on a dragonboard 410c, no regressions where found and
> no extra warnings.
>
> These two tests where already failing for other reasons:
> flip-vs-cursor-crc-atomic
> flip-vs-cursor-crc-legacy
>
> If you want to see the full log:
>
> https://people.collabora.com/~koike/drm-fixes-results.zip
>
> Thanks
> Helen
>
> >
> > In other platforms (VC4, AMD, Rockchip), there is a hidden
> > drm_framebuffer_get(new_fb)/drm_framebuffer_put(old_fb) in async_update
> > that is wrong, but I couldn't identify those here, not sure if it is hidden
> > somewhere else, but if tests fail this is probably the cause.
> >
> > Thanks!
> > Helen
> >
> > Changes in v3: None
> > Changes in v2:
> > - update CC stable and Fixes tag
> >
> >  drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> > index be13140967b4..b854f471e9e5 100644
> > --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> > +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> > @@ -502,6 +502,8 @@ static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
> >  static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
> >                                          struct drm_plane_state *new_state)
> >  {
> > +     struct drm_framebuffer *old_fb = plane->state->fb;
> > +
> >       plane->state->src_x = new_state->src_x;
> >       plane->state->src_y = new_state->src_y;
> >       plane->state->crtc_x = new_state->crtc_x;
> > @@ -524,6 +526,8 @@ static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
> >
> >       *to_mdp5_plane_state(plane->state) =
> >               *to_mdp5_plane_state(new_state);
> > +
> > +     new_state->fb = old_fb;
> >  }
> >
> >  static const struct drm_plane_helper_funcs mdp5_plane_helper_funcs = {
> >