Re: [PATCH] scsi: mq queue stall during command requeue

[Hannes Reinecke <hare@suse.de>]

On 01/19/2017 05:11 PM, Bart Van Assche wrote:
> On Thu, 2017-01-19 at 15:17 +0100, Hannes Reinecke wrote:
>> When we're hitting a busy condition in queuecommand() we need to
>> stop the hardware queue before calling blk_mq_delay_queue(); if
>> we don't blk_mq_delay_queue() will not do anything and requeue
>> will never triggered.
>>
>> Signed-off-by: Hannes Reinecke <hare@suse.com>
>> ---
>>  drivers/scsi/scsi_lib.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index e9e1e14..4b1cbc6 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -1951,8 +1951,10 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
>>  	switch (ret) {
>>  	case BLK_MQ_RQ_QUEUE_BUSY:
>>  		if (atomic_read(&sdev->device_busy) == 0 &&
>> -		    !scsi_device_blocked(sdev))
>> +		    !scsi_device_blocked(sdev)) {
>> +			blk_mq_stop_hw_queue(hctx);
>>  			blk_mq_delay_queue(hctx, SCSI_QUEUE_DELAY);
>> +		}
>>  		break;
>>  	case BLK_MQ_RQ_QUEUE_ERROR:
>>  		/*
> 
> You may want to add Fixes: 52d7f1b5c2f3 (blk-mq: Avoid that requeueing
> starts stopped queues). See also
> https://www.spinics.net/lists/linux-block/msg06144.html.
> 
Yes indeed.

But the powers that be still ponder if it should be fixed in
the SCSI stack or whether it's a generic fix for blk_mq_delay_queue().

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +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)