block: Mark bdrv_co_flush() and callers GRAPH_RDLOCK

This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_co_flush() need to hold a reader lock for the graph.

For some places, we know that they will hold the lock, but we don't have
the GRAPH_RDLOCK annotations yet. In this case, add assume_graph_lock()
with a FIXME comment. These places will be removed once everything is
properly annotated.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230203152202.49054-8-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index c9fb809..4ba72c6 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -185,7 +185,7 @@
     return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
 }
 
-static int coroutine_fn cbw_co_flush(BlockDriverState *bs)
+static int coroutine_fn GRAPH_RDLOCK cbw_co_flush(BlockDriverState *bs)
 {
     if (!bs->file) {
         return 0;