Possible fb ref count issue with drm_plane_force_disable()

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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Hi,

I've been debugging omapdrm issues on top of the latest drm mainline
changes. Sometimes a drm_framebuffer ref count drops to -1 when aborting
a drm application, or unloading the modules.

The setup is very basic, just a single crtc with the crtc's primary plane.

What seems to happen is:

- App is started

- fb is created, and taken into use by omapdrm. omapdrm takes a ref to
the fb.

- the app is starts to shut down

- drm_framebuffer_remove is called

- fb->refcount.refcount > 1, so it goes to disable stuff

- drm_plane_force_disable is called for the primary plane

- drm_plane_force_disable does plane->disable_plane, which on omapdrm
puts stuff on a workqueue as plane cannot be disabled immediately

- drm_plane_force_disable calls __drm_framebuffer_unreference()

- at the end of drm_framebuffer_remove(), there's
drm_framebuffer_unreference, which causes ref count to go to zero, and
the fb to be destroyed

- a bit later, the queued work is ran, which does
drm_framebuffer_unreference(), and ref count goes to -1. Here omapdrm is
removing the ref that had been taken in the beginning.


So the explicit unref done by drm_plane_force_disable() seems a bit out
of place. I can't figure out which drm_framebuffer_reference() would be
the matching one for the unref done by drm_plane_force_disable().

Any ideas what ref is that? Or is the __drm_framebuffer_unreference()
extra in drm_plane_force_disable()?

 Tomi


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