On 01/19/2017 03:09 PM, Jens Axboe wrote:
> On 01/19/2017 04:27 AM, Hannes Reinecke wrote:
>> Hi Jens,
>>
>> upon further testing with your blk-mq-sched branch I hit a queue stall
>> during requeing:
>>
>> [ 202.340959] sd 3:0:4:1: tag#473 Send: scmd 0xffff880422e7a440
>> [ 202.340962] sd 3:0:4:1: tag#473 CDB: Test Unit Ready 00 00 00 00 00 00
>> [ 202.341161] sd 3:0:4:1: tag#473 Done: ADD_TO_MLQUEUE Result:
>> hostbyte=DID_OK driverbyte=DRIVER_OK
>> [ 202.341164] sd 3:0:4:1: tag#473 CDB: Test Unit Ready 00 00 00 00 00 00
>> [ 202.341167] sd 3:0:4:1: tag#473 Sense Key : Unit Attention [current]
>> [ 202.341171] sd 3:0:4:1: tag#473 Add. Sense: Power on, reset, or bus
>> device reset occurred
>> [ 202.341173] sd 3:0:4:1: tag#473 scsi host busy 1 failed 0
>> [ 202.341176] sd 3:0:4:1: tag#473 Inserting command ffff880422e7a440
>> into mlqueue
>>
>> ... and that is the last ever heard of that device.
>> The 'device_busy' count remains at '1' and no further commands will be
>> sent to the device.
>
> If device_busy is at 1, then it should have a command pending. Where did
> you log this - it would be bandy if you attached whatever debug patch
> you put in, so we can see where the printks are coming from. If we get a
> BUSY with nothing pending, the driver should be ensuring that the queue
> gets run again later through blk_mq_delay_queue(), for instance.
>
> When the device is stuck, does it restart if you send it IO?
>
Meanwhile I've found it.
Problem is that scsi_queue_rq() will not stop the queue when hitting a
busy condition before sending commands down to the driver, but still
calls blk_mq_delay_queue():
switch (ret) {
case BLK_MQ_RQ_QUEUE_BUSY:
if (atomic_read(&sdev->device_busy) == 0 &&
!scsi_device_blocked(sdev))
blk_mq_delay_queue(hctx, SCSI_QUEUE_DELAY);
break;
As the queue isn't stopped blk_mq_delay_queue() won't do anything,
so queue_rq() will never be called.
I've send a patch to linux-scsi.
BTW: Is it a hard requirement that the queue has to be stopped when
returning BLK_MQ_RQ_QUEUE_BUSY?
The comments indicate as such, but none of the drivers do so...
Also, blk_mq_delay_queue() is a bit odd, in that it'll only start
stopped hardware queues. I would at least document that the queue has to
be stopped when calling that.
Better still, can't we have blk_mq_delay_queue start the queues
unconditionally?
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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