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From: Hannes Reinecke <hare@suse.de>
To: Daniel Wagner <dwagner@suse.de>, linux-nvme@lists.infradead.org
Cc: linux-kernel@vger.kernel.org,
	James Smart <james.smart@broadcom.com>,
	Keith Busch <kbusch@kernel.org>, Ming Lei <ming.lei@redhat.com>,
	Sagi Grimberg <sagi@grimberg.me>, Wen Xiong <wenxiong@us.ibm.com>,
	James Smart <jsmart2021@gmail.com>
Subject: Re: [PATCH v4 6/8] nvme-fc: fix controller reset hang during traffic
Date: Wed, 4 Aug 2021 09:23:49 +0200	[thread overview]
Message-ID: <79c89923-f586-79e7-6dfd-c15ceb21f569@suse.de> (raw)
In-Reply-To: <20210802112658.75875-7-dwagner@suse.de>

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,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer

  parent reply	other threads:[~2021-08-04  7:23 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02 11:26 [PATCH RESEND v4 0/8] Handle update hardware queues and queue freeze more carefully Daniel Wagner
2021-08-02 11:26 ` [PATCH v4 1/8] nvme-fc: Update hardware queues before using them Daniel Wagner
2021-08-02 19:34   ` Himanshu Madhani
2021-08-02 11:26 ` [PATCH v4 2/8] nvme-tcp: Update number of " Daniel Wagner
2021-08-06 19:57   ` Sagi Grimberg
2021-08-09  8:52     ` Daniel Wagner
2021-08-11  1:00       ` Sagi Grimberg
2021-08-11  1:07         ` Keith Busch
2021-08-11  5:57           ` Sagi Grimberg
2021-08-11 10:25             ` Daniel Wagner
2021-08-02 11:26 ` [PATCH v4 3/8] nvme-rdma: " Daniel Wagner
2021-08-02 11:26 ` [PATCH v4 4/8] nvme-fc: Wait with a timeout for queue to freeze Daniel Wagner
2021-08-02 19:36   ` Himanshu Madhani
2021-08-02 11:26 ` [PATCH v4 5/8] nvme-fc: avoid race between time out and tear down Daniel Wagner
2021-08-02 19:38   ` Himanshu Madhani
2021-08-02 11:26 ` [PATCH v4 6/8] nvme-fc: fix controller reset hang during traffic Daniel Wagner
2021-08-02 19:39   ` Himanshu Madhani
2021-08-04  7:23   ` Hannes Reinecke [this message]
2021-08-04  8:08     ` Daniel Wagner
2021-08-11  1:05       ` Sagi Grimberg
2021-08-11 10:30         ` Daniel Wagner
2021-08-12 20:03     ` James Smart
2021-08-18 11:43       ` Daniel Wagner
2021-08-18 11:49         ` Daniel Wagner
2021-08-02 11:26 ` [PATCH v4 7/8] nvme-tcp: Unfreeze queues on reconnect Daniel Wagner
2021-08-02 11:26 ` [PATCH v4 8/8] nvme-rdma: " Daniel Wagner
2021-08-04  7:25   ` Hannes Reinecke
2021-08-06 19:59   ` Sagi Grimberg
2021-08-09  8:58     ` Daniel Wagner
  -- strict thread matches above, loose matches on Subject: below --
2021-08-02  9:14 [PATCH v4 0/8] Handle update hardware queues and queue freeze more carefully Daniel Wagner
2021-08-02  9:14 ` [PATCH v4 6/8] nvme-fc: fix controller reset hang during traffic Daniel Wagner

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