Re: [PATCH v2] mm/memory-failure: fix concurrent access issue in min_order_for_split()

["David Hildenbrand (Arm)" <david@kernel.org>]

>>  	/*
>> @@ -2862,8 +2841,7 @@ static int soft_offline_in_use_page(struct page *page)
>>  	};
>>
>>  	if (!huge && folio_test_large(folio)) {
>> -		const int new_order = min_order_for_split(folio);
>> -
>> +		lock_page(page);
>>  		/*
>>  		 * If new_order (target split order) is not 0, do not split the
>>  		 * folio at all to retain the still accessible large folio.
>> @@ -2871,8 +2849,14 @@ static int soft_offline_in_use_page(struct page *page)
>>  		 * preferred, split it to non-zero new_order like it is done in
>>  		 * memory_failure().
>>  		 */
>> -		if (new_order || try_to_split_thp_page(page, /* new_order= */ 0,
>> -						       /* release= */ true)) {
>> +		if (!min_order_for_split(folio))
>> +			ret = split_huge_page_to_order(page, 0);
>> +		else
>> +			ret = -EBUSY;
>> +		unlock_page(page);
>> +
>> +		if (ret) {
>> +			put_page(page);
>>  			pr_info("%#lx: thp split failed\n", pfn);
>>  			return -EBUSY;
> 
> Maybe return ret here? Seems a bit pointless to set ret, gate on it then not
> return it (even if result is the same)

I didn't check whether a caller actually relies on -EBUSY. So I decided to leave
the behavior unchanged.

-- 
Cheers,

David