block: Protect bs->children with graph_lock

Almost all functions that access the child links already take the graph
lock now. Add locking to the remaining users and finally annotate the
struct field itself as protected by the graph lock.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-22-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index 2ac7406..f9cf05d 100644
--- a/block.c
+++ b/block.c
@@ -2973,6 +2973,8 @@
 {
     assert(!child->bs);
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     assert(!child->next.le_prev); /* not in children list */
 
     g_free(child->name);