Re: [PATCH v4 6/8] nvme-fc: fix controller reset hang during traffic

[James Smart <jsmart2021@gmail.com>]

On 8/4/2021 12:23 AM, Hannes Reinecke wrote:
> On 8/2/21 1:26 PM, Daniel Wagner wrote:
>> From: James Smart <jsmart2021@gmail.com>
>>
>> commit fe35ec58f0d3 ("block: update hctx map when use multiple maps")
>> exposed an issue where we may hang trying to wait for queue freeze
>> during I/O. We call blk_mq_update_nr_hw_queues which may attempt to freeze
>> the queue. However we never started queue freeze when starting the
>> reset, which means that we have inflight pending requests that entered the
>> queue that we will not complete once the queue is quiesced.
>>
>> So start a freeze before we quiesce the queue, and unfreeze the queue
>> after we successfully connected the I/O queues (the unfreeze is already
>> present in the code). blk_mq_update_nr_hw_queues will be called only
>> after we are sure that the queue was already frozen.
>>
>> This follows to how the pci driver handles resets.
>>
>> This patch added logic introduced in commit 9f98772ba307 "nvme-rdma: fix
>> controller reset hang during traffic".
>>
>> Signed-off-by: James Smart <jsmart2021@gmail.com>
>> CC: Sagi Grimberg <sagi@grimberg.me>
>> [dwagner: call nvme_unfreeze() unconditionally in
>>            nvme_fc_recreate_io_queues() to match the nvme_start_freeze()]
>> Tested-by: Daniel Wagner <dwagner@suse.de>
>> Reviewed-by: Daniel Wagner <dwagner@suse.de>
>> ---
>>   drivers/nvme/host/fc.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
>> index 133b87db4f1d..b292af0fd655 100644
>> --- a/drivers/nvme/host/fc.c
>> +++ b/drivers/nvme/host/fc.c
>> @@ -2486,6 +2486,7 @@ __nvme_fc_abort_outstanding_ios(struct nvme_fc_ctrl *ctrl, bool start_queues)
>>   	 * (but with error status).
>>   	 */
>>   	if (ctrl->ctrl.queue_count > 1) {
>> +		nvme_start_freeze(&ctrl->ctrl);
>>   		nvme_stop_queues(&ctrl->ctrl);
>>   		nvme_sync_io_queues(&ctrl->ctrl);
>>   		blk_mq_tagset_busy_iter(&ctrl->tag_set,
>> @@ -2966,8 +2967,8 @@ nvme_fc_recreate_io_queues(struct nvme_fc_ctrl *ctrl)
>>   			return -ENODEV;
>>   		}
>>   		blk_mq_update_nr_hw_queues(&ctrl->tag_set, nr_io_queues);
>> -		nvme_unfreeze(&ctrl->ctrl);
>>   	}
>> +	nvme_unfreeze(&ctrl->ctrl);
>>   
>>   	ret = nvme_fc_create_hw_io_queues(ctrl, ctrl->ctrl.sqsize + 1);
>>   	if (ret)
>>
> There still is now an imbalance, as we're always calling
> 'nvme_unfreeze()' (irrespective on the number of queues), but will only
> call 'nvme_start_freeze()' if we have more than one queue.
> 
> This might lead to an imbalance on the mq_freeze_depth counter.
> Wouldn't it be better to move the call to 'nvme_start_freeze()' out of
> the if() condition to avoid the imbalance?
> 
> Cheers,

Daniel,

try this. Moves the location of the freeze and will always pair with the 
unfreeze.

--- fc.c	2021-08-12 12:33:33.273278611 -0700
+++ fc.c.new	2021-08-12 13:01:16.185817238 -0700
@@ -2965,9 +2965,10 @@ nvme_fc_recreate_io_queues(struct nvme_f
  			prior_ioq_cnt, nr_io_queues);
  		nvme_wait_freeze(&ctrl->ctrl);
  		blk_mq_update_nr_hw_queues(&ctrl->tag_set, nr_io_queues);
-		nvme_unfreeze(&ctrl->ctrl);
  	}

+	nvme_unfreeze(&ctrl->ctrl);
+
  	return 0;

  out_delete_hw_queues:
@@ -3206,6 +3207,9 @@ nvme_fc_delete_association(struct nvme_f
  	ctrl->iocnt = 0;
  	spin_unlock_irqrestore(&ctrl->lock, flags);

+	if (ctrl->ctrl.queue_count > 1)
+		nvme_start_freeze(&ctrl->ctrl);
+
  	__nvme_fc_abort_outstanding_ios(ctrl, false);

  	/* kill the aens as they are a separate path */