linux-kernel - Re: [PATCH] x86/mtrr: Remove redundant code

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Date:   Wed, 18 Oct 2023 10:41:37 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        jgross@...e.com, linux-kernel@...r.kernel.org,
        Abaci Robot <abaci@...ux.alibaba.com>
Subject: Re: [PATCH] x86/mtrr: Remove redundant code


* Jiapeng Chong <jiapeng.chong@...ux.alibaba.com> wrote:

> arch/x86/kernel/cpu/mtrr/cleanup.c:943:4: warning: Value stored to 'highest_pfn' is never read.
> 
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=6912
> Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
> ---
>  arch/x86/kernel/cpu/mtrr/cleanup.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c b/arch/x86/kernel/cpu/mtrr/cleanup.c
> index 18cf79d6e2c5..c4ec295cebbc 100644
> --- a/arch/x86/kernel/cpu/mtrr/cleanup.c
> +++ b/arch/x86/kernel/cpu/mtrr/cleanup.c
> @@ -939,8 +939,6 @@ int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
>  	if (mtrr_tom2) {
>  		range[nr_range].start = (1ULL<<(32 - PAGE_SHIFT));
>  		range[nr_range].end = mtrr_tom2 >> PAGE_SHIFT;
> -		if (highest_pfn < range[nr_range].end)
> -			highest_pfn = range[nr_range].end;
>  		nr_range++;
>  	}
>  	nr_range = x86_get_mtrr_mem_range(range, nr_range, 0, 0);

Please explain in the changelog how that redundant code got there and why 
there's no underlying bug to be concerned about.

[ I just did that myself and could share the results - but this kind of 
  analysis has to be done when submitting "cleanup" patches changing such 
  type of code ... or at least it has to be flagged, not just mindlessly 
  removing code ... ]

Thanks,

	Ingo