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Subject: Re: [PATCH] mm/memory_failure: Fix the missing pte_unmap() call
To:     Qi Zheng <zhengqi.arch@bytedance.com>, naoya.horiguchi@nec.com,
        akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        songmuchun@bytedance.com
References: <20210923122642.4999-1-zhengqi.arch@bytedance.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <7330e2e0-9dc4-e412-a821-ed62a469371d@redhat.com>
Date:   Thu, 23 Sep 2021 17:19:22 +0200
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On 23.09.21 14:26, Qi Zheng wrote:
> The paired pte_unmap() call is missing before the
> dev_pagemap_mapping_shift() returns. So fix it.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>   mm/memory-failure.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e2984c123e7e..4e5419f16fd4 100644
> --- 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;
>   }
>   
>   /*
> 

I guess this code never runs on 32bit / highmem, that's why we didn't 
notice so far.

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb