The legacy plane->fb pointer is refcounted by calling
drm_atomic_clean_old_fb().

In practice this isn't a real problem because:
- The caller in the i915 gpu reset code restores the original state
  again, which means the plane->fb pointer won't change, hence can't
  leak.
- Drivers using drm_atomic_helper_shutdown call the fbdev cleanup
  first, and that usually cleans up the fb through
  drm_remove_framebuffer, which does this correctly.
- Without fbdev the only framebuffers are from userspace, and those
  get cleaned up (again using drm_remove_framebuffer) befor the driver
  can even be unloaded.

But in i915 I've switched the cleanup sequence around so that the
_shutdown() calls happens after the drm_remove_framebuffer(), which is
how I discovered this issue.

Cc: [email protected]
Cc: [email protected]
Signed-off-by: Daniel Vetter <[email protected]>
---
 drivers/gpu/drm/drm_atomic_helper.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c 
b/drivers/gpu/drm/drm_atomic_helper.c
index b07fc30372d3..71b5f71e61e0 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -2726,6 +2726,7 @@ int drm_atomic_helper_disable_all(struct drm_device *dev,
        struct drm_plane *plane;
        struct drm_crtc_state *crtc_state;
        struct drm_crtc *crtc;
+       unsigned plane_mask = 0;
        int ret, i;
 
        state = drm_atomic_state_alloc(dev);
@@ -2768,10 +2769,14 @@ int drm_atomic_helper_disable_all(struct drm_device 
*dev,
                        goto free;
 
                drm_atomic_set_fb_for_plane(plane_state, NULL);
+               plane_mask |= BIT(drm_plane_index(plane));
+               plane->old_fb = plane->fb;
        }
 
        ret = drm_atomic_commit(state);
 free:
+       if (plane_mask)
+               drm_atomic_clean_old_fb(dev, plane_mask, ret);
        drm_atomic_state_put(state);
        return ret;
 }
-- 
2.13.2

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