node low data disk doesn't show alert

[like-inspur]

I define node low data disk for test like this，node low root disk show alert，but data disk doesn't
ALERT NodeLowDataDisk
IF ((node_filesystem_size{mountpoint="/var/lib/docker/"} - node_filesystem_free{mountpoint="/var/lib/docker/"}) / node_filesystem_size{mountpoint="/var/lib/docker/"} * 100) > 1
FOR 2m
LABELS {severity="page"}
ANNOTATIONS {DESCRIPTION="{{$labels.instance}}: Data disk usage is above 1% (current value is: {{ $value }})", SUMMARY="{{$labels.instance}}: Low data disk space"}

I find disk mount /var/lib/docker like this：
[root@master2 prometheus]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/cl-root 37G 4.0G 33G 11% /
devtmpfs 3.9G 4.0K 3.9G 1% /dev
shm 64M 0 64M 0% /dev/shm
tmpfs 3.9G 247M 3.6G 7% /run
tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
/dev/sdc 40G 26G 15G 64% /var/lib/docke