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Date:   Mon, 26 Feb 2018 09:24:40 -0700
From:   Keith Busch <keith.busch@intel.com>
To:     baegjae@gmail.com
Cc:     axboe@fb.com, hch@lst.de, sagi@grimberg.me,
        linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] nvme-multipath: fix sysfs dangerously created links
Message-ID: <20180226162440.GB10832@localhost.localdomain>
References: <20180226085123.26120-1-baegjae@gmail.com>
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On Mon, Feb 26, 2018 at 05:51:23PM +0900, baegjae@gmail.com wrote:
> From: Baegjae Sung <baegjae@gmail.com>
> 
> If multipathing is enabled, each NVMe subsystem creates a head
> namespace (e.g., nvme0n1) and multiple private namespaces
> (e.g., nvme0c0n1 and nvme0c1n1) in sysfs. When creating links for
> private namespaces, links of head namespace are used, so the
> namespace creation order must be followed (e.g., nvme0n1 ->
> nvme0c1n1). If the order is not followed, links of sysfs will be
> incomplete or kernel panic will occur.
> 
> The kernel panic was:
>   kernel BUG at fs/sysfs/symlink.c:27!
>   Call Trace:
>     nvme_mpath_add_disk_links+0x5d/0x80 [nvme_core]
>     nvme_validate_ns+0x5c2/0x850 [nvme_core]
>     nvme_scan_work+0x1af/0x2d0 [nvme_core]
> 
> Correct order
> Context A     Context B
> nvme0n1
> nvme0c0n1     nvme0c1n1
> 
> Incorrect order
> Context A     Context B
>               nvme0c1n1
> nvme0n1
> nvme0c0n1
> 
> The function of a head namespace creation is moved to maintain the
> correct order. We verified the code with or without multipathing
> using three vendors of dual-port NVMe SSDs.
> 
> Signed-off-by: Baegjae Sung <baegjae@gmail.com>

Thanks, I see what you mean on the potential ordering problem here.
Calling nvme_mpath_add_disk, though, before the 'head' has any namespace
paths available looks like you'll get a lot of 'no path available'
warnings during the bring-up. It should resolve itself shortly after,
but the warnings will be a bit alarming, right?

> ---
>  drivers/nvme/host/core.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 0fe7ea35c221..28777b7352a5 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -2844,7 +2844,7 @@ static struct nvme_ns_head *nvme_alloc_ns_head(struct nvme_ctrl *ctrl,
>  }
>  
>  static int nvme_init_ns_head(struct nvme_ns *ns, unsigned nsid,
> -		struct nvme_id_ns *id, bool *new)
> +		struct nvme_id_ns *id)
>  {
>  	struct nvme_ctrl *ctrl = ns->ctrl;
>  	bool is_shared = id->nmic & (1 << 0);
> @@ -2860,8 +2860,7 @@ static int nvme_init_ns_head(struct nvme_ns *ns, unsigned nsid,
>  			ret = PTR_ERR(head);
>  			goto out_unlock;
>  		}
> -
> -		*new = true;
> +		nvme_mpath_add_disk(head);
>  	} else {
>  		struct nvme_ns_ids ids;
>  
> @@ -2873,8 +2872,6 @@ static int nvme_init_ns_head(struct nvme_ns *ns, unsigned nsid,
>  			ret = -EINVAL;
>  			goto out_unlock;
>  		}
> -
> -		*new = false;
>  	}
>  
>  	list_add_tail(&ns->siblings, &head->list);
> @@ -2945,7 +2942,6 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
>  	struct nvme_id_ns *id;
>  	char disk_name[DISK_NAME_LEN];
>  	int node = dev_to_node(ctrl->dev), flags = GENHD_FL_EXT_DEVT;
> -	bool new = true;
>  
>  	ns = kzalloc_node(sizeof(*ns), GFP_KERNEL, node);
>  	if (!ns)
> @@ -2971,7 +2967,7 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
>  	if (id->ncap == 0)
>  		goto out_free_id;
>  
> -	if (nvme_init_ns_head(ns, nsid, id, &new))
> +	if (nvme_init_ns_head(ns, nsid, id))
>  		goto out_free_id;
>  	nvme_setup_streams_ns(ctrl, ns);
>  	
> @@ -3037,8 +3033,6 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
>  		pr_warn("%s: failed to register lightnvm sysfs group for identification\n",
>  			ns->disk->disk_name);
>  
> -	if (new)
> -		nvme_mpath_add_disk(ns->head);
>  	nvme_mpath_add_disk_links(ns);
>  	return;
>   out_unlink_ns:
> -- 
> 2.16.2
>