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

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Date:   Thu, 1 Aug 2019 09:00:13 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Qian Cai <cai@....pw>
Cc:     catalin.marinas@....com, will@...nel.org, andreyknvl@...gle.com,
        aryabinin@...tuozzo.com, glider@...gle.com, dvyukov@...gle.com,
        linux-arm-kernel@...ts.infradead.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64/mm: fix variable 'tag' set but not used

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));		\
 })