failed to mount overlayfs

[nicklgw]

I found that overlayfs can't mount the right directory. so that all data which users modified was lost.

OK:  
overlayfs:/overlay on / type overlay (rw,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work)
NG:  
overlayfs:/tmp/root on / type overlay (rw,noatime,lowerdir=/,upperdir=/tmp/root/upper,workdir=/tmp/root/work)

the issue has found by the linux team.
please see it.
http://lists.infradead.org/pipermail/linux-mtd/2016-September/069185.html

[nicklgw]

The issue has been founded by the linux team.

overlayfs does not issue a recursive rm on workdir, AFAICT you are supposed to cleanup workdir yourself before mounting.
http://lists.infradead.org/pipermail/linux-mtd/2016-September/069185.html