Re: [PATCH] kmemleak: fix kmemleak false positive report with HW tag-based kasan enable

[Andrew Morton]

On Thu, 25 Nov 2021 17:13:36 +0100 Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote:

> > > kmemleak_object *object)
> > >  static struct kmemleak_object *lookup_object(unsigned long ptr, int
> > > alias)
> > >  {
> > >       struct rb_node *rb = object_tree_root.rb_node;
> > > +     unsigned long untagged_ptr = (unsigned
> > > long)kasan_reset_tag((void *)ptr);
> > >
> > >       while (rb) {
> > >               struct kmemleak_object *object =
> > >                       rb_entry(rb, struct kmemleak_object, rb_node);
> > > -             if (ptr < object->pointer)
> > > +             unsigned long untagged_objp;
> > > +
> > > +             untagged_objp = (unsigned long)kasan_reset_tag((void
> > > *)object->pointer);
> 
> The two lines above can be squashed together.

That would make a too-long line even longer.  In fact I think it's
better to go the other way:

--- a/mm/kmemleak.c~kmemleak-fix-kmemleak-false-positive-report-with-hw-tag-based-kasan-enable-fix
+++ a/mm/kmemleak.c
@@ -384,10 +384,10 @@ static struct kmemleak_object *lookup_ob
 	unsigned long untagged_ptr = (unsigned long)kasan_reset_tag((void *)ptr);
 
 	while (rb) {
-		struct kmemleak_object *object =
-			rb_entry(rb, struct kmemleak_object, rb_node);
+		struct kmemleak_object *object;
 		unsigned long untagged_objp;
 
+		object = rb_entry(rb, struct kmemleak_object, rb_node);
 		untagged_objp = (unsigned long)kasan_reset_tag((void *)object->pointer);
 
 		if (untagged_ptr < untagged_objp)
_