Re: [PATCH] block: fix potential IO hang when turning off io_poll

[JeffleXu <jefflexu@linux.alibaba.com>]

On 2/22/21 3:12 PM, Joseph Qi wrote:
> 
> 
> On 2/22/21 2:54 PM, Jeffle Xu wrote:
>> QUEUE_FLAG_POLL flag will be cleared when turning off 'io_poll', while
>> at that moment there may be IOs stuck in hw queue uncompleted. The
>> following polling routine won't help reap these IOs, since blk_poll()
>> will return immediately because of cleared QUEUE_FLAG_POLL flag. Thus
>> these IOs will hang until they finnaly time out. The hang out can be
>> observed by 'fio --engine=io_uring iodepth=1', while turning off
>> 'io_poll' at the same time.
>>
>> To fix this, freeze and flush the request queue first when turning off
>> 'io_poll'.
>>
>> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
>> ---
>>  block/blk-sysfs.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
>> index b513f1683af0..10d74741c002 100644
>> --- a/block/blk-sysfs.c
>> +++ b/block/blk-sysfs.c
>> @@ -430,8 +430,11 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
>>  
>>  	if (poll_on)
>>  		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
>> -	else
>> +	else {
>> +		blk_mq_freeze_queue(q);
>>  		blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
>> +		blk_mq_unfreeze_queue(q);
>> +	}
>>  
>>  	return ret;
>>  }
>>
> 
> Better to place brace to 'if' as well.

Got it, thanks.


-- 
Thanks,
Jeffle