On Fri, Apr 14, 2017 at 12:24:55AM +0200, Alexandru Moise wrote: > Seeing as RB_RED is defined to be 0 in include/linux/rbtree_augmented.h > A call of this form: rb_set_parent_color(node, parent, RB_RED); > as seen in __rb_insert would only end up reassigning the parent "color" > (which is the parent pointer value cast to unsigned long) OR'd with 0. > Which would mean that nothing would really change regarding the parent's > "color". So, that would lead one to think that the diagram at case 2 showing > the grandparent's color going from black to red could not be completely > accurate > as the Linux implementation presently stands. > > Could the maintainers provide an answer as to why the below patch is the > __wrong__ thing to do? Apart from the obvious "the values of the macros > might change in the future". > > Thanks, > ../Alex > --- > lib/rbtree.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/lib/rbtree.c b/lib/rbtree.c > index 4ba2828a67c0..6b540be4dda4 100644 > --- a/lib/rbtree.c > +++ b/lib/rbtree.c > @@ -135,7 +135,6 @@ __rb_insert(struct rb_node *node, struct rb_root *root, > rb_set_parent_color(parent, gparent, RB_BLACK); > node = gparent; > parent = rb_parent(node); > - rb_set_parent_color(node, parent, RB_RED); > continue; > } >
So who would clear the bit then? The point here is (IIRC) that node is black and needs to become red.
