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>

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;