On 1/11/19 6:16 PM, Matthew Wilcox wrote: > On Fri, Jan 11, 2019 at 03:58:43PM -0500, Qian Cai wrote: >> diff --git a/lib/rbtree_test.c b/lib/rbtree_test.c >> index b7055b2a07d3..afad0213a117 100644 >> --- a/lib/rbtree_test.c >> +++ b/lib/rbtree_test.c >> @@ -345,6 +345,17 @@ static int __init rbtree_test_init(void) >> check(0); >> } >> >> + /* >> + * a little regression test to catch a bug may be introduced by >> + * 6d58452dc06 (rbtree: adjust root color in rb_insert_color() only when >> + * necessary) >> + */ >> + insert(nodes, &root); >> + nodes->rb.__rb_parent_color = RB_RED; >> + insert(nodes + 1, &root); >> + erase(nodes + 1, &root); >> + erase(nodes, &root); > > That's not a fair test! You're poking around in the data structure to > create the situation. This test would have failed before 6d58452dc06 too. > How do we create a tree that has a red parent at root, only using insert() > and erase()? > If only I knew how to reproduce this myself, I might be able to figure out how it ends up with the red root in the first place.
