Re: Re: [PATCH] mm: mempolicy: fix the wrong return value and potential pages leak of mbind

["Li Xinhai" <lixinhai.lxh@gmail.com>]

On 2019-10-31 at 02:14 Yang Shi wrote:
>
>
>On 10/30/19 9:58 AM, Yang Shi wrote:
>> The commit d883544515aa ("mm: mempolicy: make the behavior consistent
>> when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified") fixed the return
>> value of mbind() for a couple of corner cases.  But, it altered the
>> errno for some other cases, for example, mbind() should return -EFAULT
>> when part or all of the memory range specified by nodemask and maxnode
>> points  outside your accessible address space, or there was an unmapped
>> hole in the specified memory range specified by addr and len.
>>
>> Fixed this by preserving the errno returned by queue_pages_range().
>> And, the pagelist may be not empty even though queue_pages_range()
>> returns error, put the pages back to LRU since mbind_range() is not called
>> to really apply the policy so those pages should not be migrated, this
>> is also the old behavior before the problematic commit.
>Forgot fixes tag.
>
>Fixes: d883544515aa ("mm: mempolicy: make the behavior consistent when
>MPOL_MF_MOVE* and MPOL_MF_STRICT were specified")
> 
Looks good to me.
Reviewed-by: Li Xinhai <lixinhai.lxh@gmail.com>

>> Reported-by: Li Xinhai <lixinhai.lxh@gmail.com>
>> Cc: Vlastimil Babka <vbabka@suse.cz>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Mel Gorman <mgorman@techsingularity.net>
>> Cc: <stable@vger.kernel.org> v4.19 and v5.2+
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>> ---
>>   mm/mempolicy.c | 14 +++++++++-----
>>   1 file changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index 4ae967b..e08c941 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -672,7 +672,9 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
>>    * 1 - there is unmovable page, but MPOL_MF_MOVE* & MPOL_MF_STRICT were
>>    *     specified.
>>    * 0 - queue pages successfully or no misplaced page.
>> - * -EIO - there is misplaced page and only MPOL_MF_STRICT was specified.
>> + * errno - i.e. misplaced pages with MPOL_MF_STRICT specified (-EIO) or
>> + *         memory range specified by nodemask and maxnode points outside
>> + *         your accessible address space (-EFAULT)
>>    */
>>   static int
>>   queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
>> @@ -1286,7 +1288,7 @@ static long do_mbind(unsigned long start, unsigned long len,
>>     flags | MPOL_MF_INVERT, &pagelist);
>>  
>>   if (ret < 0) {
>> -	err = -EIO;
>> +	err = ret;
>>   goto up_out;
>>   }
>>  
>> @@ -1305,10 +1307,12 @@ static long do_mbind(unsigned long start, unsigned long len,
>>  
>>   if ((ret > 0) || (nr_failed && (flags & MPOL_MF_STRICT)))
>>   err = -EIO;
>> -	} else
>> -	putback_movable_pages(&pagelist);
>> -
>> +	} else {
>>   up_out:
>> +	if (!list_empty(&pagelist))
>> +	putback_movable_pages(&pagelist);
>> +	}
>> +
>>   up_write(&mm->mmap_sem);
>>   mpol_out:
>>   mpol_put(new);
>