vhdx: Require GRAPH_RDLOCK for accessing a node's parent list

This adds GRAPH_RDLOCK annotations to declare that functions accessing
the parent list of a node need to hold a reader lock for the graph. As
it happens, they already do.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230504115750.54437-12-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/vhdx.c

@@ -1506,8 +1506,9 @@ vhdx_co_writev(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
  * There are 2 headers, and the highest sequence number will represent
  * the active header
  */
-static int vhdx_create_new_headers(BlockBackend *blk, uint64_t image_size,
-                                   uint32_t log_size)
+static int coroutine_fn GRAPH_RDLOCK
+vhdx_create_new_headers(BlockBackend *blk, uint64_t image_size,
+                        uint32_t log_size)
 {
     BlockDriverState *bs = blk_bs(blk);
     BdrvChild *child;
@@ -1897,8 +1898,8 @@ static int vhdx_create_new_region_table(BlockBackend *blk,
  *    .---- ~ ----------- ~ ------------ ~ ---------------- ~ -----------.
  *   1MB
  */
-static int coroutine_fn vhdx_co_create(BlockdevCreateOptions *opts,
-                                       Error **errp)
+static int coroutine_fn GRAPH_RDLOCK
+vhdx_co_create(BlockdevCreateOptions *opts, Error **errp)
 {
     BlockdevCreateOptionsVhdx *vhdx_opts;
     BlockBackend *blk = NULL;