Re: [PATCH v2] arm64/mm: fix variable 'tag' set but not used

[Qian Cai <cai@lca.pw>]

On Thu, 2019-08-01 at 09:00 -0700, Matthew Wilcox wrote:
> On Thu, Aug 01, 2019 at 10:47:05AM -0400, Qian Cai wrote:
> 
> Given this:
> 
> > -#define __tag_set(addr, tag)	(addr)
> > +static inline const void *__tag_set(const void *addr, u8 tag)
> > +{
> > +	return addr;
> > +}
> > +
> >  #define __tag_reset(addr)	(addr)
> >  #define __tag_get(addr)		0
> >  #endif
> > @@ -301,8 +305,8 @@ static inline void *phys_to_virt(phys_addr_t x)
> >  #define page_to_virt(page)	({					
> > \
> >  	unsigned long __addr =						
> > \
> >  		((__page_to_voff(page)) | PAGE_OFFSET);			
> > \
> > -	unsigned long __addr_tag =					\
> > -		 __tag_set(__addr, page_kasan_tag(page));		\
> > +	const void *__addr_tag =					\
> > +		__tag_set((void *)__addr, page_kasan_tag(page));	\
> >  	((void *)__addr_tag);						
> > \
> >  })
> 
> Can't you simplify that macro to:
> 
>  #define page_to_virt(page)	({					\
>  	unsigned long __addr =						
> \
>  		((__page_to_voff(page)) | PAGE_OFFSET);			
> \
> -	unsigned long __addr_tag =					\
> -		 __tag_set(__addr, page_kasan_tag(page));		\
> -	((void *)__addr_tag);						
> \
> +	__tag_set((void *)__addr, page_kasan_tag(page));		\
>  })

It still need a cast or lowmem_page_address() will complain of a discarded
"const". It might be a bit harder to read when adding a cast as in,

((void *)__tag_set((void *)__addr, page_kasan_tag(page)));

But, that feel like more of a followup patch for me if ever needed.