Re: [PATCH v2] rbtree: fix the red root

[Esme]

I've been out today but return home tomorrow and can test any suggested fixes, or with different kernel settings.  Just let me know.

Esme


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âââââââ Original Message âââââââ
On Friday, January 11, 2019 7:18 PM, Qian Cai <cai@xxxxxx> wrote:

> 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.