Re: [PATCH v2 4/8] mm/memory-failure.c: fix race with changing page more robustly

[Miaohe Lin <linmiaohe@huawei.com>]

On 2022/2/18 9:13, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Wed, Feb 16, 2022 at 05:14:27PM +0800, Miaohe Lin wrote:
>> We're only intended to deal with the non-Compound page after we split thp
>> in memory_failure. However, the page could have changed compound pages due
>> to race window. If this happens, we could try again to hopefully handle the
>> page next round. Also remove unneeded orig_head. It's always equal to the
>> hpage. So we can use hpage directly and remove this redundant one.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>>  mm/memory-failure.c | 20 ++++++++++++--------
>>  1 file changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 7e205d91b2d7..d66f642888be 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1690,7 +1690,6 @@ int memory_failure(unsigned long pfn, int flags)
>>  {
>>  	struct page *p;
>>  	struct page *hpage;
>> -	struct page *orig_head;
>>  	struct dev_pagemap *pgmap;
>>  	int res = 0;
>>  	unsigned long page_flags;
>> @@ -1736,7 +1735,7 @@ int memory_failure(unsigned long pfn, int flags)
>>  		goto unlock_mutex;
>>  	}
>>  
>> -	orig_head = hpage = compound_head(p);
>> +	hpage = compound_head(p);
>>  	num_poisoned_pages_inc();
>>  
>>  	/*
>> @@ -1817,13 +1816,18 @@ int memory_failure(unsigned long pfn, int flags)
>>  	lock_page(p);
>>  
>>  	/*
>> -	 * The page could have changed compound pages during the locking.
>> -	 * If this happens just bail out.
>> +	 * We're only intended to deal with the non-Compound page here.
>> +	 * However, the page could have changed compound pages due to
>> +	 * race window. If this happens, we could try again to hopefully
>> +	 * handle the page next round.
>>  	 */
>> -	if (PageCompound(p) && compound_head(p) != orig_head) {
>> -		action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);
>> -		res = -EBUSY;
>> -		goto unlock_page;
>> +	if (PageCompound(p)) {
>> +		if (TestClearPageHWPoison(p))
>> +			num_poisoned_pages_dec();
>> +		unlock_page(p);
>> +		put_page(p);
>> +		flags &= ~MF_COUNT_INCREASED;
> 
> Could you limit the retry chance only once by using the local variable
> "retry"?  It might be very rare to hit the race more than once in a single
> error event, but just to be safe from potential infinite loop (that could be
> opened by future changes).
> 

Sure. Will do it in V3. Thanks.

> Thanks,
> Naoya Horiguchi
> 
>> +		goto try_again;
>>  	}
>>  
>>  	/*
>> -- 
>> 2.23.0