linux-kernel - Re: [PATCH 2/2] x86/mm: replace a goto by merging two if clause

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Message-ID: <20190923092231.GJ2349@hirez.programming.kicks-ass.net>
Date:   Mon, 23 Sep 2019 11:22:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     dave.hansen@...ux.intel.com, luto@...nel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/mm: replace a goto by merging two if clause

On Thu, Sep 19, 2019 at 10:08:44AM +0800, Wei Yang wrote:
> There is only one place to use good_area jump, which could be reduced by
> merging the following two if clause.
> 
> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
> ---
>  arch/x86/mm/fault.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 9d18b73b5f77..72ce6c69e195 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1390,18 +1390,17 @@ void do_user_addr_fault(struct pt_regs *regs,
>  	vma = find_vma(mm, address);
>  	if (unlikely(!vma))
>  		goto bad_area;
> -	if (likely(vma->vm_start <= address))
> -		goto good_area;
> -	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
> -		goto bad_area;
> -	if (unlikely(expand_stack(vma, address)))
> +	if (likely(vma->vm_start <= address)) {
> +		/* good area, do nothing */
> +	} else if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)) ||
> +		   unlikely(expand_stack(vma, address))) {
>  		goto bad_area;
> +	}
>  
>  	/*
>  	 * Ok, we have a good vm_area for this memory access, so
>  	 * we can handle it..
>  	 */
> -good_area:
>  	if (unlikely(access_error(hw_error_code, vma))) {
>  		bad_area_access_error(regs, hw_error_code, address, vma);
>  		return;

I find the old code far easier to read... is there any actual reason to
do this?