linux-kernel - Re: [PATCHv3] powerpc: mm: radix_tlb: rearrange the if-else block

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Message-ID: <YfQFom4xDcysN1yb@dev-arch.archlinux-ax161>
Date:   Fri, 28 Jan 2022 08:02:58 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     ndesaulniers@...gle.com, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, christophe.leroy@...roup.eu,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCHv3] powerpc: mm: radix_tlb: rearrange the if-else block

On Fri, Jan 28, 2022 at 02:17:13PM +0100, Anders Roxell wrote:
> Clang warns:
> 
> arch/powerpc/mm/book3s64/radix_tlb.c:1191:23: error: variable 'hstart' is uninitialized when used here [-Werror,-Wuninitialized]
>                                 __tlbiel_va_range(hstart, hend, pid,
>                                                   ^~~~~~
> arch/powerpc/mm/book3s64/radix_tlb.c:1175:23: note: initialize the variable 'hstart' to silence this warning
>                 unsigned long hstart, hend;
>                                     ^
>                                      = 0
> arch/powerpc/mm/book3s64/radix_tlb.c:1191:31: error: variable 'hend' is uninitialized when used here [-Werror,-Wuninitialized]
>                                 __tlbiel_va_range(hstart, hend, pid,
>                                                           ^~~~
> arch/powerpc/mm/book3s64/radix_tlb.c:1175:29: note: initialize the variable 'hend' to silence this warning
>                 unsigned long hstart, hend;
>                                           ^
>                                            = 0
> 2 errors generated.
> 
> Rework the 'if (IS_ENABLE(CONFIG_TRANSPARENT_HUGEPAGE))' so hstart/hend
> always gets initialized, this will silence the warnings. That will also
> simplify the 'else' path. Clang is getting confused with these warnings,
> but the warnings is a false-positive.
> 
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Suggested-by: Nathan Chancellor <nathan@...nel.org>
> Reviewed-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  arch/powerpc/mm/book3s64/radix_tlb.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
> index 7724af19ed7e..5172d5cec2c0 100644
> --- a/arch/powerpc/mm/book3s64/radix_tlb.c
> +++ b/arch/powerpc/mm/book3s64/radix_tlb.c
> @@ -1171,15 +1171,12 @@ static inline void __radix__flush_tlb_range(struct mm_struct *mm,
>  			}
>  		}
>  	} else {
> -		bool hflush = false;
> +		bool hflush;
>  		unsigned long hstart, hend;
>  
> -		if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> -			hstart = (start + PMD_SIZE - 1) & PMD_MASK;
> -			hend = end & PMD_MASK;
> -			if (hstart < hend)
> -				hflush = true;
> -		}
> +		hstart = (start + PMD_SIZE - 1) & PMD_MASK;
> +		hend = end & PMD_MASK;
> +		hflush = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && hstart < hend;
>  
>  		if (type == FLUSH_TYPE_LOCAL) {
>  			asm volatile("ptesync": : :"memory");
> -- 
> 2.34.1
>