linux-kernel - Re: [PATCH] linux/bitmap.h: fix BITMAP_LAST_WORD

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Message-ID: <CAHp75VeTN5AmVj5knocsRFssQ9phzCz+jTXLMKoJ9WtasAPJRQ@mail.gmail.com>
Date:   Thu, 26 Jul 2018 17:00:39 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Jonathan Corbet <corbet@....net>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        dgilbert@...hat.com, Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [PATCH] linux/bitmap.h: fix BITMAP_LAST_WORD_MASK

On Thu, Jul 26, 2018 at 1:08 PM, Wei Wang <wei.w.wang@...el.com> wrote:
> On 07/26/2018 04:48 PM, Andy Shevchenko wrote:
>>
>> On Thu, Jul 26, 2018 at 11:07 AM, Wei Wang <wei.w.wang@...el.com> wrote:
>>>
>>> The existing BITMAP_LAST_WORD_MASK macro returns 0xffffffff if nbits is
>>> 0. This patch changes the macro to return 0 when there is no bit needs to
>>> be masked.
>>>
>> Can you provide a practical example of what's going wrong before this
>> patch applied?
>>
>
> The reason of making this patch is that I saw some other software which
> ports this function and has possibilities to fall into bugs with usages
> which pass 0 to the macro.

No problems in the kernel, right?

> So I wonder if it would be necessary to make such
> changes in case we would get a similar bug. Or adding something to explain
> that "0" is not applicable to this macro as a reminder to people who would
> use it.

Comment can be added, yes.

-- 
With Best Regards,
Andy Shevchenko