Nouveau - Aug 2020 - [PATCH] drm/nouveau: Drop mutex_lock_nested for atomic

Purely conjecture, but I think the original locking inversion with the
legacy page flip code between flipping and ttm's bo move function
shoudn't exist anymore with atomic: With atomic the bo pinning and
actual modeset commit is completely separated in the code patsh.

This annotation was originally added in

commit 060810d7abaabcab282e062c595871d661561400
Author: Ben Skeggs <bskeggs at redhat.com>
Date:   Mon Jul 8 14:15:51 2013 +1000

    drm/nouveau: fix locking issues in page flipping paths

due to

commit b580c9e2b7ba5030a795aa2fb73b796523d65a78
Author: Maarten Lankhorst <m.b.lankhorst at gmail.com>
Date:   Thu Jun 27 13:48:18 2013 +0200

    drm/nouveau: make flipping lockdep safe

Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Cc: Maarten Lankhorst <m.b.lankhorst at gmail.com>
Cc: Ben Skeggs <bskeggs at redhat.com>
Cc: Dave Airlie <airlied at gmail.com>
Cc: nouveau at lists.freedesktop.org
---
I might be totally wrong, so this definitely needs testing :-)

Cheers, Daniel
---
 drivers/gpu/drm/nouveau/nouveau_bo.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c
b/drivers/gpu/drm/nouveau/nouveau_bo.c
index 7806278dce57..a7b2a9bb0ffe 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -776,7 +776,11 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo, int
evict, bool intr,
 			return ret;
 	}
 
-	mutex_lock_nested(&cli->mutex, SINGLE_DEPTH_NESTING);
+	if (drm_drv_uses_atomic_modeset(drm->dev))
+		mutex_lock(&cli->mutex);
+	else
+		mutex_lock_nested(&cli->mutex, SINGLE_DEPTH_NESTING);
+
 	ret = nouveau_fence_sync(nouveau_bo(bo), chan, true, intr);
 	if (ret == 0) {
 		ret = drm->ttm.move(chan, bo, &bo->mem, new_reg);
-- 
2.27.0

Op 02-08-2020 om 20:18 schreef Daniel Vetter:
> Purely conjecture, but I think the original locking inversion with the
> legacy page flip code between flipping and ttm's bo move function
> shoudn't exist anymore with atomic: With atomic the bo pinning and
> actual modeset commit is completely separated in the code patsh.
>
> This annotation was originally added in
>
> commit 060810d7abaabcab282e062c595871d661561400
> Author: Ben Skeggs <bskeggs at redhat.com>
> Date:   Mon Jul 8 14:15:51 2013 +1000
>
>     drm/nouveau: fix locking issues in page flipping paths
>
> due to
>
> commit b580c9e2b7ba5030a795aa2fb73b796523d65a78
> Author: Maarten Lankhorst <m.b.lankhorst at gmail.com>
> Date:   Thu Jun 27 13:48:18 2013 +0200
>
>     drm/nouveau: make flipping lockdep safe
>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Maarten Lankhorst <m.b.lankhorst at gmail.com>
> Cc: Ben Skeggs <bskeggs at redhat.com>
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: nouveau at lists.freedesktop.org
> ---
> I might be totally wrong, so this definitely needs testing :-)
>
> Cheers, Daniel
> ---
>  drivers/gpu/drm/nouveau/nouveau_bo.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c
b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index 7806278dce57..a7b2a9bb0ffe 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -776,7 +776,11 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo, int
evict, bool intr,
>  			return ret;
>  	}
>  
> -	mutex_lock_nested(&cli->mutex, SINGLE_DEPTH_NESTING);
> +	if (drm_drv_uses_atomic_modeset(drm->dev))
> +		mutex_lock(&cli->mutex);
> +	else
> +		mutex_lock_nested(&cli->mutex, SINGLE_DEPTH_NESTING);
> +
>  	ret = nouveau_fence_sync(nouveau_bo(bo), chan, true, intr);
>  	if (ret == 0) {
>  		ret = drm->ttm.move(chan, bo, &bo->mem, new_reg);
Well if you're certain it works now. :)

Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>

Ben, did you have a chance to look at this?
-Daniel

On Mon, Aug 3, 2020 at 1:22 PM Maarten Lankhorst
<maarten.lankhorst at linux.intel.com> wrote:
>
> Op 02-08-2020 om 20:18 schreef Daniel Vetter:
> > Purely conjecture, but I think the original locking inversion with the
> > legacy page flip code between flipping and ttm's bo move function
> > shoudn't exist anymore with atomic: With atomic the bo pinning and
> > actual modeset commit is completely separated in the code patsh.
> >
> > This annotation was originally added in
> >
> > commit 060810d7abaabcab282e062c595871d661561400
> > Author: Ben Skeggs <bskeggs at redhat.com>
> > Date:   Mon Jul 8 14:15:51 2013 +1000
> >
> >     drm/nouveau: fix locking issues in page flipping paths
> >
> > due to
> >
> > commit b580c9e2b7ba5030a795aa2fb73b796523d65a78
> > Author: Maarten Lankhorst <m.b.lankhorst at gmail.com>
> > Date:   Thu Jun 27 13:48:18 2013 +0200
> >
> >     drm/nouveau: make flipping lockdep safe
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > Cc: Maarten Lankhorst <m.b.lankhorst at gmail.com>
> > Cc: Ben Skeggs <bskeggs at redhat.com>
> > Cc: Dave Airlie <airlied at gmail.com>
> > Cc: nouveau at lists.freedesktop.org
> > ---
> > I might be totally wrong, so this definitely needs testing :-)
> >
> > Cheers, Daniel
> > ---
> >  drivers/gpu/drm/nouveau/nouveau_bo.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c
b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > index 7806278dce57..a7b2a9bb0ffe 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > @@ -776,7 +776,11 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object
*bo, int evict, bool intr,
> >                       return ret;
> >       }
> >
> > -     mutex_lock_nested(&cli->mutex, SINGLE_DEPTH_NESTING);
> > +     if (drm_drv_uses_atomic_modeset(drm->dev))
> > +             mutex_lock(&cli->mutex);
> > +     else
> > +             mutex_lock_nested(&cli->mutex,
SINGLE_DEPTH_NESTING);
> > +
> >       ret = nouveau_fence_sync(nouveau_bo(bo), chan, true, intr);
> >       if (ret == 0) {
> >               ret = drm->ttm.move(chan, bo, &bo->mem,
new_reg);
>
> Well if you're certain it works now. :)
>
> Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>

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