block: Mark bdrv_attach_child() GRAPH_WRLOCK

Instead of taking the writer lock internally, require callers to already
hold it when calling bdrv_attach_child_common(). These callers will
typically already hold the graph lock once the locking work is
completed, which means that they can't call functions that take it
internally.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230911094620.45040-13-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/block.c b/block.c
index f06de58a3b..369023872a 100644
--- a/block.c
+++ b/block.c
@@ -3219,8 +3219,6 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
 
     GLOBAL_STATE_CODE();
 
-    bdrv_graph_wrlock(child_bs);
-
     child = bdrv_attach_child_noperm(parent_bs, child_bs, child_name,
                                      child_class, child_role, tran, errp);
     if (!child) {
@@ -3235,9 +3233,8 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
 
 out:
     tran_finalize(tran, ret);
-    bdrv_graph_wrunlock();
 
-    bdrv_unref(child_bs);
+    bdrv_schedule_unref(child_bs);
 
     return ret < 0 ? NULL : child;
 }
@@ -3758,11 +3755,13 @@ BdrvChild *bdrv_open_child(const char *filename,
         return NULL;
     }
 
+    bdrv_graph_wrlock(NULL);
     ctx = bdrv_get_aio_context(bs);
     aio_context_acquire(ctx);
     child = bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
                               errp);
     aio_context_release(ctx);
+    bdrv_graph_wrunlock();
 
     return child;
 }