drm: Update todo.rst

Internship season is starting, let's review this. One thing that's
pending is Maxime's work to roll out drm_atomic_state pointers to all
callbacks, he said he'll remove that entry once it's all done.

v2: Fix typos (Maxime)

Acked-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210121112919.1460322-1-daniel.vetter@ffwll.ch

Documentation/gpu/todo.rst

@@ -577,20 +577,24 @@ Contact: Daniel Vetter
 
 Level: Intermediate
 
-KMS cleanups
-------------
+Object lifetime fixes
+---------------------
 
-Some of these date from the very introduction of KMS in 2008 ...
+There's two related issues here
 
-- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty
-  function tables in drivers, but before we can remove them we need to make sure
-  that all the users in helpers and drivers do correctly check for a NULL
-  vtable.
+- Cleanup up the various ->destroy callbacks, which often are all the same
+  simple code.
 
-- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the
-  drm_*_cleanup implementations and can be removed. Some tack a kfree() at the
-  end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
-  historical reasons) misnamed drm_primary_helper_destroy() function.
+- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc,
+  which results in use-after free issues on driver unload. This can be serious
+  trouble even for drivers for hardware integrated on the SoC due to
+  EPROBE_DEFERRED backoff.
+
+Both these problems can be solved by switching over to drmm_kzalloc(), and the
+various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(),
+drmm_universal_plane_alloc(), ... and so on.
+
+Contact: Daniel Vetter
 
 Level: Intermediate
 
@@ -626,8 +630,6 @@ See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
 internship task, since it only requires a virtual machine and can be sized to
 fit the available time.
 
-Contact: Daniel Vetter
-
 Level: See details
 
 Backlight Refactoring