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Date: Fri, 25 Apr 2025 16:43:36 +0200
From: Christoph Hellwig <hch@lst.de>
To: Nilay Shroff <nilay@linux.ibm.com>
Cc: linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, hch@lst.de,
	kbusch@kernel.org, hare@suse.de, sagi@grimberg.me,
	jmeneghi@redhat.com, axboe@kernel.dk, martin.petersen@oracle.com,
	gjoyce@ibm.com
Subject: Re: [RFC PATCHv2 1/3] nvme-multipath: introduce delayed removal of
 the multipath head node
Message-ID: <20250425144336.GA12179@lst.de>
References: <20250425103319.1185884-1-nilay@linux.ibm.com> <20250425103319.1185884-2-nilay@linux.ibm.com>
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In-Reply-To: <20250425103319.1185884-2-nilay@linux.ibm.com>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Apr 25, 2025 at 04:03:08PM +0530, Nilay Shroff wrote:
> @@ -4007,10 +4008,6 @@ static void nvme_ns_remove(struct nvme_ns *ns)
>  
>  	mutex_lock(&ns->ctrl->subsys->lock);
>  	list_del_rcu(&ns->siblings);
> -	if (list_empty(&ns->head->list)) {
> -		list_del_init(&ns->head->entry);
> -		last_path = true;
> -	}
>  	mutex_unlock(&ns->ctrl->subsys->lock);
>  
>  	/* guarantee not available in head->list */
> @@ -4028,8 +4025,7 @@ static void nvme_ns_remove(struct nvme_ns *ns)
>  	mutex_unlock(&ns->ctrl->namespaces_lock);
>  	synchronize_srcu(&ns->ctrl->srcu);
>  
> -	if (last_path)
> -		nvme_mpath_shutdown_disk(ns->head);
> +	nvme_mpath_shutdown_disk(ns->head);

This now removes the head list deletion from the first critical
section into nvme_mpath_shutdown_disk.  I remember we had to do it
the way it currently is done because we were running into issues
otherwise, the commit history might help a bit with what the issues
were.

> +	if (a == &dev_attr_delayed_removal_secs.attr) {
> +		struct nvme_ns_head *head = dev_to_ns_head(dev);
> +		struct gendisk *disk = dev_to_disk(dev);
> +
> +		/*
> +		 * This attribute is only valid for head node and non-fabric
> +		 * setup.
> +		 */
> +		if (!nvme_disk_is_ns_head(disk) ||
> +				test_bit(NVME_NSHEAD_FABRICS, &head->flags))
> +			return 0;
> +	}

Didn't we say we also want to allow fabrics to use it if explicitly
configured?