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

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Message-Id: <20211127162028.07d1a9fc392d91e7d234daae@linux-foundation.org>
Date:   Sat, 27 Nov 2021 16:20:28 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        Nicholas Tang (鄭秦輝) 
        <nicholas.tang@...iatek.com>,
        James Hsu ( 徐慶薰) 
        <James.Hsu@...iatek.com>,
        Yee Lee (李建誼) 
        <Yee.Lee@...iatek.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] kmemleak: fix kmemleak false positive report with HW
 tag-based kasan enable

On Thu, 25 Nov 2021 17:13:36 +0100 Andrey Konovalov <andreyknvl@...il.com> 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)
_