[Devel] [PATCH rh8] ploop: Update cached bat_entries before bio completion

[Kirill Tkhai]

Konstantin, could you please commit this?

On 19.02.2020 15:05, Kirill Tkhai wrote:
> https://jira.sw.ru/browse/PSBM-101499
> 
> On 19.02.2020 15:03, Kirill Tkhai wrote:
>> Right after data_bio->end_io is called, it's expected
>> a subsequent read returns written data. But there is
>> a race between ploop_bat_write_complete() and ploop_map():
>>
>> WRITE					READ
>> ploop_bat_write_complete()
>>   data_bio->end_io()
>> 					write submitter sees write completion
>> 					next submittion is READ
>> 					ploop_map()
>> 					  check BAT --- sees zero BAT entry
>> 					  zero_fill_bio()
>>   update BAT
>>
>> So, the order has to be vise versa: first is to update BAT cache,
>> second is to call data_bio->end_io().
>>
>> https://jira.sw.ru/browse/PSBM-100788
>>
>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>> ---
>>  drivers/md/dm-ploop-map.c |   21 ++++++++++++---------
>>  1 file changed, 12 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
>> index a67656b2b01e..4ca0f8e83400 100644
>> --- a/drivers/md/dm-ploop-map.c
>> +++ b/drivers/md/dm-ploop-map.c
>> @@ -623,6 +623,18 @@ static void ploop_bat_write_complete(struct bio *bio)
>>  
>>  	track_bio(ploop, bio);
>>  
>> +	if (!bio->bi_status) {
>> +		/*
>> +		 * Success: now update local BAT copy. We could do this
>> +		 * from our delayed work, but we want to publish new
>> +		 * mapping in the fastest way. This must be done before
>> +		 * data bios completion, since right after we complete
>> +		 * a bio, subsequent read wants to see written data
>> +		 * (ploop_map() wants to see not zero bat_entries[.]).
>> +		 */
>> +		ploop_advance_local_after_bat_wb(ploop, piwb, true);
>> +	}
>> +
>>  	spin_lock_irqsave(&piwb->lock, flags);
>>  	piwb->completed = true;
>>  	piwb->bi_status = bio->bi_status;
>> @@ -644,15 +656,6 @@ static void ploop_bat_write_complete(struct bio *bio)
>>  		complete_cow(cow, bio->bi_status);
>>  	}
>>  
>> -	if (!piwb->bi_status) {
>> -		/*
>> -		 * Success: now update local BAT copy. We could do this
>> -		 * from our delayed work, but we want to publish new
>> -		 * mapping in the fastest way.
>> -		 */
>> -		ploop_advance_local_after_bat_wb(ploop, piwb, true);
>> -	}
>> -
>>  	/*
>>  	 * In case of update BAT is failed, dst_clusters will be
>>  	 * set back to holes_bitmap on last put_piwb().
>>
>>
> 
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