nvme: put ns_head ref if namespace fails allocation

mainline inclusion
from mainline-v5.1-rc1
commit a63b8370
category: bugfix
bugzilla: NA
CVE: NA
Link: https://gitee.com/openeuler/kernel/issues/I1WGZE

--------------------------------

In case nvme_alloc_ns fails after we initialize ns_head but before we
add the ns to the controller namespaces list we need to explicitly put
the ns_head reference because when we teardown the controller we
won't find it, causing us to leak a dangling subsystem eventually.
Signed-off-by: NSagi Grimberg <sagi@grimberg.me>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Reviewed-by: NChao Leng <lengchao@huawei.com>
Reviewed-by: NJike Cheng <chengjike.cheng@huawei.com>
Signed-off-by: NLijie <lijie34@huawei.com>
Reviewed-by: NTao Hou <houtao1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/nvme/host/core.c

@@ -3247,6 +3247,7 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
 	mutex_lock(&ctrl->subsys->lock);
 	list_del_rcu(&ns->siblings);
 	mutex_unlock(&ctrl->subsys->lock);
+	nvme_put_ns_head(ns->head);
  out_free_id:
 	kfree(id);
  out_free_queue: