Re: [PATCH v2 03/10] nvme-multipath: add error handling support for add_disk()

From: Hannes Reinecke <hare@suse.de>
To: Luis Chamberlain <mcgrof@kernel.org>,
	axboe@kernel.dk, colyli@suse.de, kent.overstreet@gmail.com,
	kbusch@kernel.org, sagi@grimberg.me, vishal.l.verma@intel.com,
	dan.j.williams@intel.com, dave.jiang@intel.com,
	ira.weiny@intel.com, konrad.wilk@oracle.com,
	roger.pau@citrix.com, boris.ostrovsky@oracle.com,
	jgross@suse.com, sstabellini@kernel.org, minchan@kernel.org,
	ngupta@vflare.org, senozhatsky@chromium.org
Cc: xen-devel@lists.xenproject.org, nvdimm@lists.linux.dev,
	linux-nvme@lists.infradead.org, linux-bcache@vger.kernel.org,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 03/10] nvme-multipath: add error handling support for add_disk()
Date: Tue, 28 Sep 2021 07:39:54 +0200	[thread overview]
Message-ID: <85d33b80-1d54-67ba-47f9-0298093b6d80@suse.de> (raw)
In-Reply-To: <20210927220039.1064193-4-mcgrof@kernel.org>

On 9/28/21 12:00 AM, Luis Chamberlain wrote:
> We never checked for errors on add_disk() as this function
> returned void. Now that this is fixed, use the shiny new
> error handling.
> 
> Since we now can tell for sure when a disk was added, move
> setting the bit NVME_NSHEAD_DISK_LIVE only when we did
> add the disk successfully.
> 
> Nothing to do here as the cleanup is done elsewhere. We take
> care and use test_and_set_bit() because it is protects against
> two nvme paths simultaneously calling device_add_disk() on the
> same namespace head.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>   drivers/nvme/host/multipath.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index e8ccdd398f78..35cace4f3f5f 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -496,13 +496,22 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
>   static void nvme_mpath_set_live(struct nvme_ns *ns)
>   {
>   	struct nvme_ns_head *head = ns->head;
> +	int rc;
>   
>   	if (!head->disk)
>   		return;
>   
> +	/*
> +	 * test_and_set_bit() is used because it is protecting against two nvme
> +	 * paths simultaneously calling device_add_disk() on the same namespace
> +	 * head.
> +	 */
>   	if (!test_and_set_bit(NVME_NSHEAD_DISK_LIVE, &head->flags)) {
> -		device_add_disk(&head->subsys->dev, head->disk,
> -				nvme_ns_id_attr_groups);
> +		rc = device_add_disk(&head->subsys->dev, head->disk,
> +				     nvme_ns_id_attr_groups);
> +		if (rc)
> +			return;
> +		set_bit(NVME_NSHEAD_DISK_LIVE, &head->flags);
>   		nvme_add_ns_head_cdev(head);
>   	}
>   
> Errm.
Setting the same bit twice?
And shouldn't you unset the bit if 'device_add_disk()' fails?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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