Re: [PATCHv5] nvme: allow to re-attach namespaces after all paths are down

From: Christoph Hellwig <hch@lst.de>
To: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	Keith Busch <keith.busch@wdc.com>,
	linux-nvme@lists.infradead.org
Subject: Re: [PATCHv5] nvme: allow to re-attach namespaces after all paths are down
Date: Tue, 8 Jun 2021 18:42:47 +0200	[thread overview]
Message-ID: <20210608164247.GA12430@lst.de> (raw)
In-Reply-To: <20210607133435.138525-1-hare@suse.de>

While I do like the look, I don't see how this could actually work:

>  	} else {
>  		ret = -EINVAL;
> -		if (!is_shared || !head->shared) {
> +		/*
> +		 * If multipath is enabled we might hit an ns head with no
> +		 * paths, but that doesn't indicate it's a shared namespace.
> +		 */
> +		if (!list_empty(&head->list) && (!is_shared || !head->shared)) {
>  			dev_err(ctrl->device,
>  				"Duplicate unshared namespace %d\n", nsid);
>  			goto out_put_ns_head;

When we get here with an existing ns_head with no namespaces attached
to it, we can assume it once had namespaces attached to it.  Because
of that NVME_NSHEAD_DISK_LIVE will be set, and we'll never add the
disk for it again.  Even if we did add the disk again what prevents
adding a disk and removing one from racing with each other?

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