linux-kernel - Re: [PATCH 06/11] nvmet-fcloop: track rport with ref counting

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Message-ID: <1ee44bb6-df3c-4903-9bdd-0c7728500c18@suse.de>
Date: Fri, 28 Feb 2025 08:29:55 +0100
From: Hannes Reinecke <hare@...e.de>
To: Daniel Wagner <wagi@...nel.org>, James Smart <james.smart@...adcom.com>,
 Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
 Chaitanya Kulkarni <kch@...dia.com>
Cc: Keith Busch <kbusch@...nel.org>, linux-nvme@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/11] nvmet-fcloop: track rport with ref counting

On 2/26/25 19:45, Daniel Wagner wrote:
> The rport object is created via nvme_fc_register_remote and freed
> via nvme_fc_unregister_remoteport. That means after the port is
> unregistered nothing should use it. Thus ensure with refcounting
> that there is no user left before the unregister step.
> 
> Signed-off-by: Daniel Wagner <wagi@...nel.org>
> ---
>   drivers/nvme/target/fcloop.c | 53 ++++++++++++++++++++++++++------------------
>   1 file changed, 32 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/nvme/target/fcloop.c b/drivers/nvme/target/fcloop.c
> index 2269b4d20af2ef9bb423617b94a5f5326ea124bd..d64f5fba136e13c9e4e545acecd905c31542d442 100644
> --- a/drivers/nvme/target/fcloop.c
> +++ b/drivers/nvme/target/fcloop.c
> @@ -223,8 +223,12 @@ struct fcloop_rport {
>   	spinlock_t			lock;
>   	struct list_head		ls_list;
>   	struct work_struct		ls_work;
> +	struct kref			ref;
>   };
>   
> +static int fcloop_rport_get(struct fcloop_rport *rport);
> +static void fcloop_rport_put(struct fcloop_rport *rport);
> +
>   struct fcloop_tport {
>   	struct nvmet_fc_target_port	*targetport;
>   	struct nvme_fc_remote_port	*remoteport;
> @@ -346,6 +350,7 @@ fcloop_rport_lsrqst_work(struct work_struct *work)
>   		spin_lock(&rport->lock);
>   	}
>   	spin_unlock(&rport->lock);
> +	fcloop_rport_put(rport);
>   }
>   
>   static int
> @@ -365,7 +370,8 @@ fcloop_h2t_ls_req(struct nvme_fc_local_port *localport,
>   		spin_lock(&rport->lock);
>   		list_add_tail(&tls_req->ls_list, &rport->ls_list);
>   		spin_unlock(&rport->lock);
> -		queue_work(nvmet_wq, &rport->ls_work);
> +		if (queue_work(nvmet_wq, &rport->ls_work))
> +			fcloop_rport_get(rport);

Same argument than previously: don't we need to remove 'tls_req' from 
the list on failure?

>   		return ret;
>   	}
>   
> @@ -398,7 +404,8 @@ fcloop_h2t_xmt_ls_rsp(struct nvmet_fc_target_port *targetport,
>   		spin_lock(&rport->lock);
>   		list_add_tail(&tls_req->ls_list, &rport->ls_list);
>   		spin_unlock(&rport->lock);
> -		queue_work(nvmet_wq, &rport->ls_work);
> +		if (queue_work(nvmet_wq, &rport->ls_work))
> +			fcloop_rport_get(rport);

Same here.

>   	}
>   
>   	return 0;
> @@ -1078,9 +1085,6 @@ fcloop_localport_delete(struct nvme_fc_local_port *localport)
>   static void
>   fcloop_remoteport_delete(struct nvme_fc_remote_port *remoteport)
>   {
> -	struct fcloop_rport *rport = remoteport->private;
> -
> -	flush_work(&rport->ls_work);
>   }

Empty function.

>   
>   static void
> @@ -1386,6 +1390,8 @@ fcloop_create_remote_port(struct device *dev, struct device_attribute *attr,
>   
>   	/* success */
>   	rport = remoteport->private;
> +	kref_init(&rport->ref);
> +
>   	rport->remoteport = remoteport;
>   	rport->targetport = (nport->tport) ?  nport->tport->targetport : NULL;
>   	if (nport->tport) {
> @@ -1418,21 +1424,30 @@ __unlink_remote_port(struct fcloop_nport *nport)
>   	return rport;
>   }
>   
> -static int
> -__remoteport_unreg(struct fcloop_nport *nport, struct fcloop_rport *rport)
> +static void
> +fcloop_remoteport_unreg(struct kref *ref)
>   {
> -	int ret;
> +	struct fcloop_rport *rport =
> +		container_of(ref, struct fcloop_rport, ref);
> +	struct fcloop_nport *nport;
>   
> -	if (!rport) {
> -		ret = -EALREADY;
> -		goto out;
> -	}
> +	nport = rport->nport;
> +	nvme_fc_unregister_remoteport(rport->remoteport);
>   
> -	ret = nvme_fc_unregister_remoteport(rport->remoteport);
> -out:
>   	/* nport ref put: remoteport */
>   	fcloop_nport_put(nport);
> -	return ret;
> +}
> +
> +static int
> +fcloop_rport_get(struct fcloop_rport *rport)
> +{
> +	return kref_get_unless_zero(&rport->ref);
> +}
> +
> +static void
> +fcloop_rport_put(struct fcloop_rport *rport)
> +{
> +	kref_put(&rport->ref, fcloop_remoteport_unreg);
>   }
>   
>   static ssize_t
> @@ -1468,8 +1483,7 @@ fcloop_delete_remote_port(struct device *dev, struct device_attribute *attr,
>   	if (!nport)
>   		return -ENOENT;
>   
> -	ret = __remoteport_unreg(nport, rport);
> -
> +	fcloop_rport_put(rport);
>   	fcloop_nport_put(nport);
>   
>   	return ret ? ret : count;
> @@ -1717,10 +1731,7 @@ static void __exit fcloop_exit(void)
>   		spin_unlock_irqrestore(&fcloop_lock, flags);
>   
>   		fcloop_tport_put(tport);
> -
> -		ret = __remoteport_unreg(nport, rport);
> -		if (ret)
> -			pr_warn("%s: Failed deleting remote port\n", __func__);
> +		fcloop_rport_put(rport);
>   
>   		spin_lock_irqsave(&fcloop_lock, flags);
>   	}
> 

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich