Hi, i have a question/issue related to multiattach feature in cinder

i have an openstack cluster and i have configured multiattach in the openstack cinder now when i create 1 volume (with volume type multiattach) and attach it to 2 instances test1 and test2
on test1

sudo mkfs -t ext4 /dev/sdb

sudo mkdir /mnt/mydisk

sudo mount /dev/sdb /mnt/mydisk

touch /mnt/mydisk/shared_file echo "This is some shared content" | sudo tee /mnt/mydisk/shared_file

on test2

sudo mkdir /mnt/mydisk
sudo mount /dev/sdb /mnt/mydisk
ls /mnt/mydisk/
cat /mnt/mydisk/shared_file

i can see the shared_file now when i add new files on test1 im not able to see it on test2 untill i unmount the volume with directory and mount the directory again to the volume on test2.

what could be the solution for it? how can i make the volume share datas instantly between all the instances connected to the volume

i have tried with ext4 and xfs file system

Hope to hear from you soon
Thank you!