block: Mark bdrv_filter_child() and callers GRAPH_RDLOCK

This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_filter_child() need to hold a reader lock for the graph because it
accesses bs->file/backing.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231027155333.420094-12-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index bb322df..499b147 100644
--- a/block.c
+++ b/block.c
@@ -8491,8 +8491,8 @@
     return found;
 }
 
-static BlockDriverState *bdrv_do_skip_filters(BlockDriverState *bs,
-                                              bool stop_on_explicit_filter)
+static BlockDriverState * GRAPH_RDLOCK
+bdrv_do_skip_filters(BlockDriverState *bs, bool stop_on_explicit_filter)
 {
     BdrvChild *c;