drm/amd/display: Fix handling of plane refcount

[Why]
The mechanism to backup and restore plane states doesn't maintain
refcount, which can cause issues if the refcount of the plane changes
in between backup and restore operations, such as memory leaks if the
refcount was supposed to go down, or double frees / invalid memory
accesses if the refcount was supposed to go up.

[How]
Cache and re-apply current refcount when restoring plane states.

Cc: [email protected]
Reviewed-by: Josip Pavic <[email protected]>
Signed-off-by: Joshua Aberback <[email protected]>
Signed-off-by: Hamza Mahfooz <[email protected]>
Tested-by: Daniel Wheeler <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: Joshua Aberback

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -3141,7 +3141,10 @@ static void restore_planes_and_stream_state(
 		return;
 
 	for (i = 0; i < status->plane_count; i++) {
+		/* refcount will always be valid, restore everything else */
+		struct kref refcount = status->plane_states[i]->refcount;
 		*status->plane_states[i] = scratch->plane_states[i];
+		status->plane_states[i]->refcount = refcount;
 	}
 	*stream = scratch->stream_state;
 }