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Subject: Re: [PATCH] mm/memory_failure: Fix the missing pte_unmap() call
To:     David Hildenbrand <david@redhat.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>
 <7330e2e0-9dc4-e412-a821-ed62a469371d@redhat.com>
From:   Qi Zheng <zhengqi.arch@bytedance.com>
Message-ID: <7a93c298-fd78-1963-a9f6-b4a7191bf747@bytedance.com>
Date:   Thu, 23 Sep 2021 23:30:01 +0800
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On 9/23/21 11:19 PM, David Hildenbrand wrote:
> 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.

I guess so too.

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

Thanks,
Qi