Re: [PATCH 7/7] blk-mq: don't use the requeue list to queue flush commands

[Christoph Hellwig <hch@lst.de>]

On Sun, Apr 16, 2023 at 02:01:30PM -0700, Bart Van Assche wrote:
> On 4/16/23 13:09, Christoph Hellwig wrote:
>> diff --git a/block/blk-flush.c b/block/blk-flush.c
>> index 69e9806f575455..231d3780e74ad1 100644
>> --- a/block/blk-flush.c
>> +++ b/block/blk-flush.c
>> @@ -188,7 +188,9 @@ static void blk_flush_complete_seq(struct request *rq,
>>     	case REQ_FSEQ_DATA:
>>   		list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
>> -		blk_mq_add_to_requeue_list(rq, 0);
>> +		spin_lock(&q->requeue_lock);
>> +		list_add_tail(&rq->queuelist, &q->flush_list);
>> +		spin_unlock(&q->requeue_lock);
>>   		blk_mq_kick_requeue_list(q);
>>   		break;
>
> At least the SCSI core can call blk_flush_complete_seq() from interrupt 
> context so I don't think the above code is correct. The call chain is as 
> follows:

All callers of blk_flush_complete_seq already disable interrupts when
taking mq_flush_lock.  No need to disable interrupts again for a nested
lock then.