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

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Date:   Sat, 10 Apr 2021 09:00:33 +0200
From:   Mihai Moldovan <ionic@...ic.de>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kconfig: nconf: stop endless search-up loops

* 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.



Mihai