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

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Message-ID: <2eca94ce-4e26-aff6-240d-39baf1a9cc36@bytedance.com>
Date:   Fri, 24 Sep 2021 10:24:06 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     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 9/24/21 7:17 AM, 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?

Yes, and I see this neater version has merged into your mm tree,
thanks. :)

> 
> +++ 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:
>   	pte_unmap(pte);
>   	return ret;
>   }
> _
>