drm/ttm: Fix spinlock imbalance

This imbalance may cause hangs when TTM is trying to swap out a buffer
that is already on the delayed delete list.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -1834,6 +1834,7 @@ static int ttm_bo_swapout(struct ttm_mem_shrink *shrink)
 			spin_unlock(&glob->lru_lock);
 			(void) ttm_bo_cleanup_refs(bo, false, false, false);
 			kref_put(&bo->list_kref, ttm_bo_release_list);
+			spin_lock(&glob->lru_lock);
 			continue;
 		}