linux-kernel - Re: [PATCH v2] kconfig: nconf: stop endless search-up loops

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Date:   Sat, 10 Apr 2021 18:12:54 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Mihai Moldovan <ionic@...ic.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kconfig: nconf: stop endless search-up loops

On Sat, Apr 10, 2021 at 4:00 PM Mihai Moldovan <ionic@...ic.de> wrote:
>
> * On 4/10/21 7:47 AM, Masahiro Yamada wrote:
> > On Sun, Mar 28, 2021 at 6:52 PM Mihai Moldovan <ionic@...ic.de> wrote:
> >> +               if ((index == -1) && (index == match_start))
> >> +                       return -1;
> >
> > We know 'index' is -1 in the second comparison.
> > So, you can also write like this:
> >
> >        if (match_start == -1 && index == -1)
> >                 return -1;
>
> I know, but I sided for the other form for semantic reasons - this more closely
> directly describes what we actually care about (both being the same value and
> either one being -1).
>
>
> > But, it is not the correct fix, either.
> >
> > The root cause of the bug is match_start
> > becoming -1.
> >
> >
> > The following is the correct way to fix the bug
> > without increasing the number of lines.
> >
> >
> >
> > diff --git a/scripts/kconfig/nconf.c b/scripts/kconfig/nconf.c
> > index e0f965529166..af814b39b876 100644
> > [...]
> > +       match_start = (match_start + items_num) % items_num;
> >         index = match_start;
> > -       index = (index + items_num) % items_num;
>
> This is probably more elegant and fixes two issues at the same time: match_start
> becoming -1 or n (which is likewise invalid, but was implicitly handled through
> the remainder operation).
>
> No objections from my side.


Could you send v3 please?

Then, I will apply it.



-- 
Best Regards
Masahiro Yamada