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

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Date: Tue, 2 Jan 2024 15:32:13 -0500
From: Gregory Price <gregory.price@...verge.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Gregory Price <gourry.memverge@...il.com>, linux-mm@...ck.org,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
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Subject: Re: [PATCH v5 03/11] mm/mempolicy: refactor sanitize_mpol_flags for
 reuse

On Tue, Jan 02, 2024 at 05:09:55PM +0800, Huang, Ying wrote:
> 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);
> }

was concerned with silent truncation of (*mode) (int) to short.

*shrug* happy to change it

~Gregory