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SubjectRe: [PATCH V2 4/4] arm64/mm: Drop local variable vm_fault_t from __do_page_fault()
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On 06/04/2019 08:26 PM, Catalin Marinas wrote:
> 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().

Sure.

>
>> 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.
>

TBH the proposed one seems clearer as it separates effect (vma->vm_start > addr)
from required permission check (vma->vm_flags & VM_GROWSDOWN) and required action
(expand_stack(vma, addr)). But I am happy to change as you have mentioned if that
is preferred.

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