drm/ttm: fix kref count mess in ttm_bo_move_to_lru_tail

Fixes the following scenario:

1. Page table bo allocated in vram and linked to man->lru.
   tbo->list_kref.refcount=2
2. Page table bo is swapped out and removed from man->lru.
   tbo->list_kref.refcount=1
3. Command submission from userspace.  Page table bo is moved
   to vram.  ttm_bo_move_to_lru_tail() link it to man->lru and
   don't increase the kref count.
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Flora Cui <Flora.Cui@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/ttm/ttm_bo.c

@@ -230,22 +230,13 @@ EXPORT_SYMBOL(ttm_bo_del_sub_from_lru);
 
 void ttm_bo_move_to_lru_tail(struct ttm_buffer_object *bo)
 {
-	struct ttm_bo_device *bdev = bo->bdev;
-	struct ttm_mem_type_manager *man;
+	int put_count = 0;
 
 	lockdep_assert_held(&bo->resv->lock.base);
 
-	if (bo->mem.placement & TTM_PL_FLAG_NO_EVICT) {
-		list_del_init(&bo->swap);
-		list_del_init(&bo->lru);
-
-	} else {
-		if (bo->ttm && !(bo->ttm->page_flags & TTM_PAGE_FLAG_SG))
-			list_move_tail(&bo->swap, &bo->glob->swap_lru);
-
-		man = &bdev->man[bo->mem.mem_type];
-		list_move_tail(&bo->lru, &man->lru);
-	}
+	put_count = ttm_bo_del_from_lru(bo);
+	ttm_bo_list_ref_sub(bo, put_count, true);
+	ttm_bo_add_to_lru(bo);
 }
 EXPORT_SYMBOL(ttm_bo_move_to_lru_tail);