Re: [PATCH V2 4/4] arm64/mm: Drop local variable vm_fault_t from __do_page_fault()

[Catalin Marinas]

On Thu, Jun 06, 2019 at 10:24:01AM +0530, Anshuman Khandual wrote:
> On 06/04/2019 08:26 PM, Catalin Marinas wrote:
> > On Mon, Jun 03, 2019 at 12:11:25PM +0530, Anshuman Khandual wrote:
> >> 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.

Not bothered really. You can leave them as in your proposal (I was just
seeing the VM_GROWSDOWN check tightly coupled with the expand_stack(),
it's fine either way).

-- 
Catalin