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From:   baegjae@gmail.com
To:     keith.busch@intel.com, axboe@fb.com, hch@lst.de, sagi@grimberg.me,
        baegjae@gmail.com
Cc:     linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [PATCH] nvme-multipath: fix sysfs dangerously created links
Date:   Mon, 26 Feb 2018 17:51:23 +0900
Message-Id: <20180226085123.26120-1-baegjae@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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>
---
 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