linux-kernel - Re: [PATCH] arm/mm: fix compiler warning in pmdp

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Date:	Wed, 11 Feb 2015 14:06:17 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Andre Przywara <andre.przywara@....com>, catalin.marinas@....com,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm/mm: fix compiler warning in pmdp_invalidate() (in
 -next)

On Fri, 30 Jan 2015 16:40:15 +0000 Russell King - ARM Linux <linux@....linux.org.uk> wrote:

> On Fri, Jan 30, 2015 at 04:37:32PM +0000, Andre Przywara wrote:
> > Commit ff61d185f4e7 ("mm: convert p[te|md]_mknonnuma and remaining
> > page table manipulations") removed a check in
> > mm/pgtable-generic.c:pmdp_invalidate(), which leaves the
> > pmd_mknotpresent macro the only user of the entry variable.
> > For ARM/LPAE we use a constant 0 without referencing the argument to
> > mark this condition, so the entry variable is no longer used here:
> > 
> > mm/pgtable-generic.c: In function 'pmdp_invalidate':
> > mm/pgtable-generic.c:195:8: warning: unused variable 'entry' [-Wunused-variable]
> >   pmd_t entry = *pmdp;
> >         ^
> > 
> > Replace the ARM macro implementation with a static inline function to
> > get rid of this warning.
> >  
> > Signed-off-by: Andre Przywara <andre.przywara@....com>
> > ---
> > Hi Andrew,
> > 
> > Mel mentioned that I should send that simple fix below to you to
> > merge it with his original mmotm patch:
> > mm-convert-p_mknonnuma-and-remaining-page-table-manipulations.patch
> > The commit message above contains the mmotm-reference to this patch,
> > which will break when it hits mainline.
> > 
> > Can you consider this? Given that's only a warning fix I am also
> > happy with resending it after -rc1, if you reckon that this arch/arm
> > change should not go via mmotm.
> 
> This isn't correct though.
> 
> >  /* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
> > -#define pmd_mknotpresent(pmd)	(__pmd(0))
> > +static inline pmd_t pmd_mknotpresent(pmd_t pmd)
> > +{
> > +	return 0;
> > +}
> 
> typedef struct { pmdval_t pmd; } pmd_t;
> 
> typedef u32 pmdval_t;
> 
> "0" is not compatible with pmd_t when STRICT_MM_TYPECHECKS is enabled.

This?

--- a/arch/arm/include/asm/pgtable-3level.h~mm-convert-p_mknonnuma-and-remaining-page-table-manipulations-fix-fix
+++ a/arch/arm/include/asm/pgtable-3level.h
@@ -259,7 +259,7 @@ PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
 /* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
 static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 {
-	return 0;
+	return __pmd(0);
 }
 
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)

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