I was having the same issue, I was trying and failing to delete
/usr/local/tomcat/data
with the error rm: cannot remove/usr/local/tomcat/data’: Device or resource busy`
until I noticed that df -h said
/dev/vda3 20G 172M 20G 1% /usr/local/tomcat/data
that is, I had a partition mounted to that point. Mystery solved.