Background process still exists after execute juicefs umount

[Roay]

# juicefs -V
juicefs version 0.15.2 (2021-07-07 4c168477c)
# ./juicefs  mount redis://:tst123456@localhost:6379/0 /root/jfs/mountDir/ -d 
2021/07/26 11:23:16.985866 juicefs[114780] <INFO>: Meta address: redis://@localhost:6379/0
2021/07/26 11:23:16.987085 juicefs[114780] <WARNING>: AOF is not enabled, you may lose data if Redis is not shutdown properly.
2021/07/26 11:23:16.987176 juicefs[114780] <INFO>: Ping redis: 64.615µs
2021/07/26 11:23:16.987515 juicefs[114780] <INFO>: Data use s3://jfs/tst/
2021/07/26 11:23:16.987657 juicefs[114780] <INFO>: Disk cache (/var/jfsCache/b0d9d10d-a3d6-4bd4-938c-64125a554003/): capacity (1024 MB), free ratio (10%), max pending pages (15)
2021/07/26 11:23:17.493177 juicefs[114780] <INFO>: OK, tst is ready at /root/jfs/mountDir/
# 
# cd /root/jfs/mountDir/
# ../../juicefs-0.15.2/juicefs umount /root/jfs/mountDir/
2021-07-26 11:24:12.170114 I | fusermount: failed to unmount /root/jfs/mountDir: Device or resource busy
exit status 1
# ../../juicefs-0.15.2/juicefs umount /root/jfs/mountDir/ -f
# cd ..
# ll mountDir/
total 0
# ps -ef | grep juicefs
root     114796      1  0 11:23 ?        00:00:00 ./juicefs mount redis://:tst123456@localhost:6379/0 /root/jfs/mountDir -d
root     114939   3340  0 11:24 pts/0    00:00:00 grep --color=auto juicefs

[davies]

When someone is using the mountpoint (you are using it as the current dir), the mount process should NOT exit until it's clean (all fds are close and no one is using the it).

So, this is a feature rather than a bug.