You can do this without rebooting in CentOS 7. Assuming your disk is /dev/vda and standard RHEL/CentOS partitioning:
# fdisk /dev/vda
p to print your initial partition table.
d (delete) followed by
2 to delete the existing partition definition (partition 1 is usually /boot and partition 2 is usually the root partition).
n (new) followed by
p (primary) followed by
2 to re-create partition number 2 and
enter to accept the start block and
enter again to accept the end block which is defaulted to the end of the disk.
t (type) then
8e to change the new partition type to "Linux LVM".
p to print your new partition table and make sure the start block matches what was in the initial partition table printed above.
w to write the partition table to disk. You will see an error about
Device or resource busy which you can ignore.
Update kernel in-memory partition table
After changing your partition table, run the following command to update the kernel in-memory partition table:
# partx -u /dev/vda
Resize physical volume
Resize the PV to recognize the extra space
# pvresize /dev/vda2
Resize LV and filesystem
In this command
centos is the PV,
root is the LV and
/dev/vda2 is the partition that was extended. Use
lvs commands to see your physical and logical volume names if you don't know them. The
-r option in this command resizes the filesystem appropriately so you don't have to call
# lvextend -r centos/root /dev/vda2