diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 61854be..e223e37 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -78,9 +78,9 @@
     int snapshot_error;
 } BDRVCopyBeforeWriteState;
 
-static coroutine_fn int cbw_co_preadv(
-        BlockDriverState *bs, int64_t offset, int64_t bytes,
-        QEMUIOVector *qiov, BdrvRequestFlags flags)
+static int coroutine_fn GRAPH_RDLOCK
+cbw_co_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
+              QEMUIOVector *qiov, BdrvRequestFlags flags)
 {
     return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
 }
@@ -172,11 +172,9 @@
     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
 }
 
-static coroutine_fn int cbw_co_pwritev(BlockDriverState *bs,
-                                       int64_t offset,
-                                       int64_t bytes,
-                                       QEMUIOVector *qiov,
-                                       BdrvRequestFlags flags)
+static coroutine_fn GRAPH_RDLOCK
+int cbw_co_pwritev(BlockDriverState *bs, int64_t offset, int64_t bytes,
+                   QEMUIOVector *qiov, BdrvRequestFlags flags)
 {
     int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
     if (ret < 0) {
@@ -266,6 +264,8 @@
     BdrvChild *file;
     int ret;
 
+    assume_graph_lock(); /* FIXME */
+
     /* TODO: upgrade to async loop using AioTask */
     while (bytes) {
         int64_t cur_bytes;