linux-kernel - Re: [PATCH] mm/memory_failure: Fix the missing pte

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Date:   Fri, 24 Sep 2021 09:31:02 +0900
From:   Naoya Horiguchi <naoya.horiguchi@...ux.dev>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Qi Zheng <zhengqi.arch@...edance.com>, naoya.horiguchi@....com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        songmuchun@...edance.com
Subject: Re: [PATCH] mm/memory_failure: Fix the missing pte_unmap() call

On Thu, Sep 23, 2021 at 04:17:38PM -0700, Andrew Morton wrote:
> On Thu, 23 Sep 2021 20:26:42 +0800 Qi Zheng <zhengqi.arch@...edance.com> wrote:
> 
> > The paired pte_unmap() call is missing before the
> > dev_pagemap_mapping_shift() returns. So fix it.
> > 
> > ...
> >
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -306,6 +306,7 @@ static unsigned long dev_pagemap_mapping_shift(struct page *page,
> >  		struct vm_area_struct *vma)
> >  {
> >  	unsigned long address = vma_address(page, vma);
> > +	unsigned long ret = 0;
> >  	pgd_t *pgd;
> >  	p4d_t *p4d;
> >  	pud_t *pud;
> > @@ -330,10 +331,12 @@ static unsigned long dev_pagemap_mapping_shift(struct page *page,
> >  		return PMD_SHIFT;
> >  	pte = pte_offset_map(pmd, address);
> >  	if (!pte_present(*pte))
> > -		return 0;
> > +		goto unmap;
> >  	if (pte_devmap(*pte))
> > -		return PAGE_SHIFT;
> > -	return 0;
> > +		ret = PAGE_SHIFT;
> > +unmap:
> > +	pte_unmap(pte);
> > +	return ret;
> >  }
> >  
> 
> This is neater?
> 
> +++ a/mm/memory-failure.c
> @@ -330,11 +330,8 @@ static unsigned long dev_pagemap_mapping
>  	if (pmd_devmap(*pmd))
>  		return PMD_SHIFT;
>  	pte = pte_offset_map(pmd, address);
> -	if (!pte_present(*pte))
> -		goto unmap;
> -	if (pte_devmap(*pte))
> +	if (pte_present(*pte) && pte_devmap(*pte))
>  		ret = PAGE_SHIFT;
> -unmap:

This neater one looks good to me.

Acked-by: Naoya Horiguchi <naoya.horiguchi@....com>