linux-kernel - Re: [PATCH] arm64: fix pte_unmap() -Wunused-but-set-variable

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Date:   Mon, 29 Apr 2019 17:49:23 +0100
From:   Will Deacon <will.deacon@....com>
To:     Qian Cai <cai@....pw>
Cc:     catalin.marinas@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: fix pte_unmap() -Wunused-but-set-variable

On Fri, Apr 26, 2019 at 09:28:42PM -0400, Qian Cai wrote:
> Many compilation warnings due to pte_unmap() compiles away. Fixed it by
> making it an static inline function.
> 
> mm/gup.c: In function 'gup_pte_range':
> mm/gup.c:1727:16: warning: variable 'ptem' set but not used
> [-Wunused-but-set-variable]
> mm/gup.c: At top level:
> mm/memory.c: In function 'copy_pte_range':
> mm/memory.c:821:24: warning: variable 'orig_dst_pte' set but not used
> [-Wunused-but-set-variable]
> mm/memory.c:821:9: warning: variable 'orig_src_pte' set but not used
> [-Wunused-but-set-variable]
> mm/swap_state.c: In function 'swap_ra_info':
> mm/swap_state.c:641:15: warning: variable 'orig_pte' set but not used
> [-Wunused-but-set-variable]
> mm/madvise.c: In function 'madvise_free_pte_range':
> mm/madvise.c:318:9: warning: variable 'orig_pte' set but not used
> [-Wunused-but-set-variable]
> 
> Also, remove pte_unmap_nested() as nobody uses it anymore since the
> commit ece0e2b6406a ("mm: remove pte_*map_nested()").

Can you post that as a separate patch which also removes
pte_offset_map_nested(), please?

> Signed-off-by: Qian Cai <cai@....pw>
> ---
>  arch/arm64/include/asm/pgtable.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index de70c1eabf33..7543e345e078 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -478,6 +478,8 @@ static inline phys_addr_t pmd_page_paddr(pmd_t pmd)
>  	return __pmd_to_phys(pmd);
>  }
>  
> +static inline void pte_unmap(pte_t *pte) { }

Hmm, is this guaranteed to stop the compiler from warning? Assuming the
pte_unmap() call is inlined, I'd expect it to keep complaining. What
compiler are you using?

Also, there are a bunch of other architectures that I would expect to have
this same issue because they defined pte_unmap() exactly the same way.

Will