Re: [PATCH 1/4] mm: vm_page_prot: update with WRITE_ONCE/READ_ONCE

["Hillf Danton" <hillf.zj@alibaba-inc.com>]

Hey Andrea
> 
> @@ -111,13 +111,16 @@ static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
>  void vma_set_page_prot(struct vm_area_struct *vma)
>  {
>  	unsigned long vm_flags = vma->vm_flags;
> +	pgprot_t vm_page_prot;
> 
> -	vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
> +	vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
>  	if (vma_wants_writenotify(vma)) {

Since vma->vm_page_prot is currently used in vma_wants_writenotify(), is 
it possible that semantic change is introduced here with local variable? 

thanks
Hillf
>  		vm_flags &= ~VM_SHARED;
> -		vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot,
> -						     vm_flags);
> +		vm_page_prot = vm_pgprot_modify(vma->vm_page_prot,
> +						vm_flags);
>  	}
> +	/* remove_protection_ptes reads vma->vm_page_prot without mmap_sem */
> +	WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
>  }
> 

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