[RFC PATCHv2 1/3] nvme-multipath: introduce delayed removal of the multipath head node

[Christoph Hellwig]

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?