linux-kernel - Re: [PATCH v5 03/11] mm/mempolicy: refactor sanitize_mpol

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Date: Tue, 02 Jan 2024 17:09:55 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Gregory Price <gregory.price@...verge.com>
Cc: Gregory Price <gourry.memverge@...il.com>,  <linux-mm@...ck.org>,
  <linux-doc@...r.kernel.org>,  <linux-fsdevel@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>,  <linux-api@...r.kernel.org>,
  <x86@...nel.org>,  <akpm@...ux-foundation.org>,  <arnd@...db.de>,
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  <mhocko@...nel.org>,  <tj@...nel.org>,  <corbet@....net>,
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  <sthanneeru@...ron.com>,  <emirakhur@...ron.com>,  <Hasan.Maruf@....com>,
  <seungjun.ha@...sung.com>
Subject: Re: [PATCH v5 03/11] mm/mempolicy: refactor sanitize_mpol_flags for
 reuse

Gregory Price <gregory.price@...verge.com> writes:

> On Tue, Dec 26, 2023 at 02:05:35AM -0500, Gregory Price wrote:
>> On Wed, Dec 27, 2023 at 04:39:29PM +0800, Huang, Ying wrote:
>> > Gregory Price <gourry.memverge@...il.com> writes:
>> > 
>> > > +	unsigned short mode = (*mode_arg & ~MPOL_MODE_FLAGS);
>> > > +
>> > > +	*flags = *mode_arg & MPOL_MODE_FLAGS;
>> > > +	*mode_arg = mode;
>> > 
>> > It appears that it's unnecessary to introduce a local variable to split
>> > mode/flags.  Just reuse the original code?
>> > 
>
> Revisiting during fixes: Note the change from int to short.
>
> I chose to make this explicit because validate_mpol_flags takes a short.
>
> I'm fairly sure changing it back throws a truncation warning.

Why something like below doesn't work?

int sanitize_mpol_flags(int *mode, unsigned short *flags)
{
        *flags = *mode & MPOL_MODE_FLAGS;
        *mode &= ~MPOL_MODE_FLAGS;

        return validate_mpol_flags(*mode, flags);
}

--
Best Regards,
Huang, Ying