linux-kernel - Re: [PATCH V2 4/4] arm64/mm: Drop local variable vm_fault_t from __do_page

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Date:   Tue, 4 Jun 2019 15:56:12 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH V2 4/4] arm64/mm: Drop local variable vm_fault_t from
 __do_page_fault()

On Mon, Jun 03, 2019 at 12:11:25PM +0530, Anshuman Khandual wrote:
> __do_page_fault() is over complicated with multiple goto statements. This
> cleans up the code flow and while there drops local variable vm_fault_t.

I'd change the subject as well here to something like refactor or
simplify __do_page_fault().

> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 4bb65f3..41fa905 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -397,37 +397,29 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re
>  static vm_fault_t __do_page_fault(struct mm_struct *mm, unsigned long addr,
>  			   unsigned int mm_flags, unsigned long vm_flags)
>  {
> -	struct vm_area_struct *vma;
> -	vm_fault_t fault;
> +	struct vm_area_struct *vma = find_vma(mm, addr);
>  
> -	vma = find_vma(mm, addr);
> -	fault = VM_FAULT_BADMAP;
>  	if (unlikely(!vma))
> -		goto out;
> -	if (unlikely(vma->vm_start > addr))
> -		goto check_stack;
> +		return VM_FAULT_BADMAP;
>  
>  	/*
>  	 * Ok, we have a good vm_area for this memory access, so we can handle
>  	 * it.
>  	 */
> -good_area:
> +	if (unlikely(vma->vm_start > addr)) {
> +		if (!(vma->vm_flags & VM_GROWSDOWN))
> +			return VM_FAULT_BADMAP;
> +		if (expand_stack(vma, addr))
> +			return VM_FAULT_BADMAP;
> +	}

You could have a single return here:

	if (unlikely(vma->vm_start > addr) &&
	    (!(vma->vm_flags & VM_GROWSDOWN) || expand_stack(vma, addr)))
		return VM_FAULT_BADMAP;

Not sure it's any clearer though.

-- 
Catalin