[PATCH v2] m68k: Avoid -Wunused-but-set-parameter in clear_user_page()

[PATCH v2] m68k: Avoid -Wunused-but-set-parameter in clear_user_page()

[Thomas Weißschuh]

The loop in clear_user_pages() iterates over all pages and calls
clear_user_page() for each of them. During the loop "vaddr" is modified.
However on m68k clear_user() is a macro which does not use "vaddr".
The compiler sees a variable which is modified but never used and emits
a warning for that:

include/linux/highmem.h: In function 'clear_user_pages':
include/linux/highmem.h:234:63: warning: parameter 'vaddr' set but not used [-Wunused-but-set-parameter=]
    static inline void clear_user_pages(void *addr, unsigned long vaddr,

Other architectures use an inline function for clear_user_page() which
avoids the warning. This is not possible on m68k, as dlush_dcache_page()
is another macro which is not yet defined where clear_user_page() is
defined. Including cacheflush_mm.h will trigger recursive and lots of
other issues.

So hide the warning with a cast to (void) instead.

While we are here, do the same for copy_user_page().

Fixes: 62a9f5a85b98 ("mm: introduce clear_pages() and clear_user_pages()")
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Changes in v2:
- Put parens around vaddr.
- Link to v1: https://patch.msgid.link/20260524-m68k-clear_user_page-v1-1-4c950668842e@weissschuh.net
---
 arch/m68k/include/asm/page_mm.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/m68k/include/asm/page_mm.h b/arch/m68k/include/asm/page_mm.h
index ed782609ca41..0971a0651d49 100644
--- a/arch/m68k/include/asm/page_mm.h
+++ b/arch/m68k/include/asm/page_mm.h
@@ -55,10 +55,12 @@ static inline void clear_page(void *page)
 #define clear_user_page(addr, vaddr, page)	\
 	do {	clear_page(addr);		\
 		flush_dcache_page(page);	\
+		(void)(vaddr);			\
 	} while (0)
 #define copy_user_page(to, from, vaddr, page)	\
 	do {	copy_page(to, from);		\
 		flush_dcache_page(page);	\
+		(void)(vaddr);			\
 	} while (0)
 
 extern unsigned long m68k_memoffset;

---
base-commit: eed108edc1170404bbef9e7d0189d18a3cc354f5
change-id: 20260523-m68k-clear_user_page-bf8063063f90

Best regards,
--  
Thomas Weißschuh <linux@weissschuh.net>

Re: [PATCH v2] m68k: Avoid -Wunused-but-set-parameter in clear_user_page()

[Andrew Morton]

On Mon, 25 May 2026 10:33:52 +0200 Thomas Weißschuh <linux@weissschuh.net> wrote:

> The loop in clear_user_pages() iterates over all pages and calls
> clear_user_page() for each of them. During the loop "vaddr" is modified.
> However on m68k clear_user() is a macro which does not use "vaddr".
> The compiler sees a variable which is modified but never used and emits
> a warning for that:
> 
> include/linux/highmem.h: In function 'clear_user_pages':
> include/linux/highmem.h:234:63: warning: parameter 'vaddr' set but not used [-Wunused-but-set-parameter=]
>     static inline void clear_user_pages(void *addr, unsigned long vaddr,
> 
> Other architectures use an inline function for clear_user_page() which
> avoids the warning. This is not possible on m68k, as dlush_dcache_page()
> is another macro which is not yet defined where clear_user_page() is
> defined. Including cacheflush_mm.h will trigger recursive and lots of
> other issues.
> 
> So hide the warning with a cast to (void) instead.
> 
> While we are here, do the same for copy_user_page().
> 

As with sparc, can this be addressed by converting these macros into
static inline C functions?

> --- a/arch/m68k/include/asm/page_mm.h
> +++ b/arch/m68k/include/asm/page_mm.h
> @@ -55,10 +55,12 @@ static inline void clear_page(void *page)
>  #define clear_user_page(addr, vaddr, page)	\
>  	do {	clear_page(addr);		\
>  		flush_dcache_page(page);	\
> +		(void)(vaddr);			\
>  	} while (0)
>  #define copy_user_page(to, from, vaddr, page)	\
>  	do {	copy_page(to, from);		\
>  		flush_dcache_page(page);	\
> +		(void)(vaddr);			\
>  	} while (0)
>  
>  extern unsigned long m68k_memoffset;

Re: [PATCH v2] m68k: Avoid -Wunused-but-set-parameter in clear_user_page()

[Geert Uytterhoeven]

Hi Andrew, Thomas,

On Mon, 25 May 2026 at 21:54, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Mon, 25 May 2026 10:33:52 +0200 Thomas Weißschuh <linux@weissschuh.net> wrote:
> > The loop in clear_user_pages() iterates over all pages and calls
> > clear_user_page() for each of them. During the loop "vaddr" is modified.
> > However on m68k clear_user() is a macro which does not use "vaddr".
> > The compiler sees a variable which is modified but never used and emits
> > a warning for that:
> >
> > include/linux/highmem.h: In function 'clear_user_pages':
> > include/linux/highmem.h:234:63: warning: parameter 'vaddr' set but not used [-Wunused-but-set-parameter=]
> >     static inline void clear_user_pages(void *addr, unsigned long vaddr,
> >
> > Other architectures use an inline function for clear_user_page() which
> > avoids the warning. This is not possible on m68k, as dlush_dcache_page()
> > is another macro which is not yet defined where clear_user_page() is
> > defined. Including cacheflush_mm.h will trigger recursive and lots of
> > other issues.
> >
> > So hide the warning with a cast to (void) instead.
> >
> > While we are here, do the same for copy_user_page().
> >
>
> As with sparc, can this be addressed by converting these macros into
> static inline C functions?

That would fail for similar reasons as on sparc: flush_dcache_page() is
not yet defined, and trying to include <asm/page.h> causes include hell.

> > --- a/arch/m68k/include/asm/page_mm.h
> > +++ b/arch/m68k/include/asm/page_mm.h
> > @@ -55,10 +55,12 @@ static inline void clear_page(void *page)
> >  #define clear_user_page(addr, vaddr, page)   \
> >       do {    clear_page(addr);               \
> >               flush_dcache_page(page);        \
> > +             (void)(vaddr);                  \
> >       } while (0)
> >  #define copy_user_page(to, from, vaddr, page)        \
> >       do {    copy_page(to, from);            \
> >               flush_dcache_page(page);        \
> > +             (void)(vaddr);                  \
> >       } while (0)
> >
> >  extern unsigned long m68k_memoffset;

People are starting to report this, now gcc-16 is getting more
widespread use.

Andrew: can you please take this, or shall I queue it for m68k fixes
(I don't have any other fixes at the moment)?

Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Thanks!

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v2] m68k: Avoid -Wunused-but-set-parameter in clear_user_page()

[Andrew Morton]

On Wed, 1 Jul 2026 11:48:35 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> > > --- a/arch/m68k/include/asm/page_mm.h
> > > +++ b/arch/m68k/include/asm/page_mm.h
> > > @@ -55,10 +55,12 @@ static inline void clear_page(void *page)
> > >  #define clear_user_page(addr, vaddr, page)   \
> > >       do {    clear_page(addr);               \
> > >               flush_dcache_page(page);        \
> > > +             (void)(vaddr);                  \
> > >       } while (0)
> > >  #define copy_user_page(to, from, vaddr, page)        \
> > >       do {    copy_page(to, from);            \
> > >               flush_dcache_page(page);        \
> > > +             (void)(vaddr);                  \
> > >       } while (0)
> > >
> > >  extern unsigned long m68k_memoffset;
> 
> People are starting to report this, now gcc-16 is getting more
> widespread use.
> 
> Andrew: can you please take this, or shall I queue it for m68k fixes
> (I don't have any other fixes at the moment)?
> 
> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Sorry, this fell through a crack.  I've queued it for 7.2-rcX,
cc:stable.

Re: [PATCH v2] m68k: Avoid -Wunused-but-set-parameter in clear_user_page()

[Geert Uytterhoeven]

Hi Andrew,

On Thu, 2 Jul 2026 at 01:12, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 1 Jul 2026 11:48:35 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > --- a/arch/m68k/include/asm/page_mm.h
> > > > +++ b/arch/m68k/include/asm/page_mm.h
> > > > @@ -55,10 +55,12 @@ static inline void clear_page(void *page)
> > > >  #define clear_user_page(addr, vaddr, page)   \
> > > >       do {    clear_page(addr);               \
> > > >               flush_dcache_page(page);        \
> > > > +             (void)(vaddr);                  \
> > > >       } while (0)
> > > >  #define copy_user_page(to, from, vaddr, page)        \
> > > >       do {    copy_page(to, from);            \
> > > >               flush_dcache_page(page);        \
> > > > +             (void)(vaddr);                  \
> > > >       } while (0)
> > > >
> > > >  extern unsigned long m68k_memoffset;
> >
> > People are starting to report this, now gcc-16 is getting more
> > widespread use.
> >
> > Andrew: can you please take this, or shall I queue it for m68k fixes
> > (I don't have any other fixes at the moment)?
> >
> > Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
>
> Sorry, this fell through a crack.  I've queued it for 7.2-rcX,
> cc:stable.

Thanks a lot!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds