linux-kernel - Re: [PATCHv2] powerpc: mm: radix_tlb: rearrange the if-else block

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Message-ID: <c6beb8a8-ecf3-1c17-f685-f5e69cd6265a@csgroup.eu>
Date:   Fri, 28 Jan 2022 10:14:02 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Anders Roxell <anders.roxell@...aro.org>,
        "nathan@...nel.org" <nathan@...nel.org>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCHv2] powerpc: mm: radix_tlb: rearrange the if-else block



Le 28/01/2022 à 11:08, Anders Roxell a écrit :
> 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>
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> ---
>   arch/powerpc/mm/book3s64/radix_tlb.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
> index 7724af19ed7e..7d65965a0688 100644
> --- a/arch/powerpc/mm/book3s64/radix_tlb.c
> +++ b/arch/powerpc/mm/book3s64/radix_tlb.c
> @@ -1174,12 +1174,9 @@ static inline void __radix__flush_tlb_range(struct mm_struct *mm,
>   		bool hflush = false;

You should then remove the default initialisation of hflush to false 
which has become pointless.

With that fixed,

Reviewed-by: Christophe Leroy <christophe.leroy@...roup.eu>


>   		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");