bdrv_drop_intermediate() calls BdrvChildRole.update_filename(). That may poll, thus changing the graph, which potentially breaks the QLIST_FOREACH_SAFE() loop.
Just keep the whole subtree drained. This is probably the right thing to do anyway (dropping nodes while the subtree is not drained seems wrong). Signed-off-by: Max Reitz <mre...@redhat.com> --- block.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/block.c b/block.c index a06f07347f..96b3dc7d53 100644 --- a/block.c +++ b/block.c @@ -4493,6 +4493,7 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base, int ret = -EIO; bdrv_ref(top); + bdrv_subtree_drained_begin(top); if (!top->drv || !base->drv) { goto exit; @@ -4564,6 +4565,7 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base, ret = 0; exit: + bdrv_subtree_drained_end(top); bdrv_unref(top); return ret; } -- 2.21.0