Online check of ext4:
If your filesystem is located on a logical volume (LVM) then I assume you can make a snapshot and do a check of that.
Make SS:
lvcreate --snapshot --size 1G --name lv_root_SS --chunksize 4k /dev/VG1/lv_root
EXT4 check:
e2fsck -f /dev/dm-3
Remove SS:
lvremove --yes VG1/lv_root_SS