Re: [PATCH v2 04/10] block.c: bdrv_replace_child_noperm: first remove the child, and then call ->detach()

Unfortunately this patch is not safe: theoretically ->detach can call bdrv_unapply_subtree_drain, and if it polls, will can call a bh that for example reads the graph, finding it in an inconsistent state, since it is between the two writes QLIST_REMOVE(child, next_parent); and QLIST_REMOVE(child, n

[PATCH v2 04/10] block.c: bdrv_replace_child_noperm: first remove the child, and then call ->detach()

Doing the opposite can make ->detach() (more precisely bdrv_unapply_subtree_drain() in bdrv_child_cb_detach) undo the subtree_drain just performed to protect the removal of the child from the graph, thus making the fully-enabled assert_bdrv_graph_writable fail. Note that assert_bdrv_graph_writable