block: Protect bs->parents with graph_lock

Almost all functions that access the parent link already take the graph
lock now. Add locking to the remaining user in a test case and finally
annotate the struct field itself as protected by the graph lock.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-21-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

include/block/block_int-common.h

@@ -1043,7 +1043,7 @@ struct BdrvChild {
     bool quiesced_parent;
 
     QLIST_ENTRY(BdrvChild) next;
-    QLIST_ENTRY(BdrvChild) next_parent;
+    QLIST_ENTRY(BdrvChild GRAPH_RDLOCK_PTR) next_parent;
 };
 
 /*
@@ -1180,7 +1180,7 @@ struct BlockDriverState {
     BdrvChild *backing;
     BdrvChild *file;
 
-    QLIST_HEAD(, BdrvChild) parents;
+    QLIST_HEAD(, BdrvChild GRAPH_RDLOCK_PTR) parents;
 
     QDict *options;
     QDict *explicit_options;

tests/unit/test-block-iothread.c

@@ -471,11 +471,16 @@ static void test_sync_op(const void *opaque)
     BlockDriverState *bs;
     BdrvChild *c;
 
+    GLOBAL_STATE_CODE();
+
     blk = blk_new(qemu_get_aio_context(), BLK_PERM_ALL, BLK_PERM_ALL);
     bs = bdrv_new_open_driver(&bdrv_test, "base", BDRV_O_RDWR, &error_abort);
     bs->total_sectors = 65536 / BDRV_SECTOR_SIZE;
     blk_insert_bs(blk, bs, &error_abort);
+
+    bdrv_graph_rdlock_main_loop();
     c = QLIST_FIRST(&bs->parents);
+    bdrv_graph_rdunlock_main_loop();
 
     blk_set_aio_context(blk, ctx, &error_abort);
     aio_context_acquire(ctx);