Hi Jens
Thanks for your kindly response.
On 2/12/19 7:20 AM, Jens Axboe wrote:
> On 2/11/19 4:15 PM, Jens Axboe wrote:
>> On 2/11/19 8:59 AM, Jens Axboe wrote:
>>> On 2/10/19 10:41 PM, Jianchao Wang wrote:
>>>> When requeue, if RQF_DONTPREP, rq has contained some driver
>>>> specific data, so insert it to hctx dispatch list to avoid any
>>>> merge. Take scsi as example, here is the trace event log (no
>>>> io scheduler, because RQF_STARTED would prevent merging),
>>>>
>>>> kworker/0:1H-339 [000] ...1 2037.209289: block_rq_insert: 8,0 R 4096
>>>> () 32768 + 8 [kworker/0:1H]
>>>> scsi_inert_test-1987 [000] .... 2037.220465: block_bio_queue: 8,0 R
>>>> 32776 + 8 [scsi_inert_test]
>>>> scsi_inert_test-1987 [000] ...2 2037.220466: block_bio_backmerge: 8,0 R
>>>> 32776 + 8 [scsi_inert_test]
>>>> kworker/0:1H-339 [000] .... 2047.220913: block_rq_issue: 8,0 R 8192
>>>> () 32768 + 16 [kworker/0:1H]
>>>> scsi_inert_test-1996 [000] ..s1 2047.221007: block_rq_complete: 8,0 R ()
>>>> 32768 + 8 [0]
>>>> scsi_inert_test-1996 [000] .Ns1 2047.221045: block_rq_requeue: 8,0 R ()
>>>> 32776 + 8 [0]
>>>> kworker/0:1H-339 [000] ...1 2047.221054: block_rq_insert: 8,0 R 4096
>>>> () 32776 + 8 [kworker/0:1H]
>>>> kworker/0:1H-339 [000] ...1 2047.221056: block_rq_issue: 8,0 R 4096
>>>> () 32776 + 8 [kworker/0:1H]
>>>> scsi_inert_test-1986 [000] ..s1 2047.221119: block_rq_complete: 8,0 R ()
>>>> 32776 + 8 [0]
>>>>
>>>> (32768 + 8) was requeued by scsi_queue_insert and had RQF_DONTPREP.
>>>> Then it was merged with (32776 + 8) and issued. Due to RQF_DONTPREP,
>>>> the sdb only contained the part of (32768 + 8), then only that part
>>>> was completed. The lucky thing was that scsi_io_completion detected
>>>> it and requeued the remaining part. So we didn't get corrupted data.
>>>> However, the requeue of (32776 + 8) is not expected.
>>>
>>> Good catch, but how about something like this? Makes it more integrated,
>>> I think that's cleaner.
>>
>> This is probably better (and safer):
>
> Here's the one I wanted to send, not a half done one. Maybe I'll be
> luckier this time around?
>
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8f5b533764ca..35e6aba52808 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -737,12 +737,21 @@ static void blk_mq_requeue_work(struct work_struct
> *work)
> spin_unlock_irq(&q->requeue_lock);
>
> list_for_each_entry_safe(rq, next, &rq_list, queuelist) {
> - if (!(rq->rq_flags & RQF_SOFTBARRIER))
> + if (!(rq->rq_flags & (RQF_SOFTBARRIER | RQF_DONTPREP)))
> continue;
>
> rq->rq_flags &= ~RQF_SOFTBARRIER;
> list_del_init(&rq->queuelist);
> - blk_mq_sched_insert_request(rq, true, false, false);
> +
> + /*
> + * If RQF_DONTPREP is set, rq may contain some driver
> + * specific data. Insert it to hctx dispatch list to avoid
> + * any merge.
> + */
> + if (rq->rq_flags & RQF_DONTPREP)
> + blk_mq_request_bypass_insert(rq, false);
> + else
> + blk_mq_sched_insert_request(rq, true, false, false);
> }
>
> while (!list_empty(&rq_list)) {
>
The test is OK.
And I will send out the V2 based on this.
Thanks
Jianchao
