Doing the opposite can make adding the child node to a non-drained node,
as apply_subtree_drain is only done in ->attach() and thus make
assert_bdrv_graph_writable fail.
This can happen for example during a transaction rollback (test 245,
test_io_with_graph_changes):
1. a node is removed from the graph, thus it is undrained
2. then something happens, and we need to roll back the transactions
through tran_abort()
3. at this point, the current code would first attach the undrained node
to the graph via QLIST_INSERT_HEAD, and then call ->attach() that
will take care of restoring the drain with apply_subtree_drain(),
leaving the node undrained between the two operations.
Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com>
---
block.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/block.c b/block.c
index 29de2b62b5..fb5bc3077a 100644
--- a/block.c
+++ b/block.c
@@ -2879,8 +2879,6 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
}
if (new_bs) {
- assert_bdrv_graph_writable(new_bs);
- QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
/*
* Detaching the old node may have led to the new node's
@@ -2897,6 +2895,10 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
if (child->klass->attach) {
child->klass->attach(child);
}
+
+ assert_bdrv_graph_writable(new_bs);
+ QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
+
}
/*
--
2.31.1
