[LEDE-DEV] overlayfs + ubifs: power cut results in "failed to create directory /overlay/work/work (errno: 17); mounting read-only"

[Richard Weinberger]

Rafał,

On 06.09.2016 12:46, Rafał Miłecki wrote:
> Hi,
> 
> In LEDE/OpenWrt we use UBI with two volumes: "rootfs" and "rootfs_data". With
> rootfs mounted at / we mount rootfs_data volume at /overlay and then use
> overlayfs to combine these two.
> 
> 1) Before:
> /dev/root on / type squashfs (ro,relatime)
> /dev/ubi0_1 on /overlay type ubifs (rw,noatime)
> 
> 2) Mounting overlayfs
> mount("overlayfs:/overlay", "/mnt", "overlay", MS_NOATIME, "lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work")
> 
> 3) After:
> /dev/root on / type squashfs (ro,relatime)
> /dev/ubi0_1 on /overlay type ubifs (rw,noatime)
> overlayfs:/overlay on /mnt type overlay (ro,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work)
> 
> It works fine as long as there aren't unexpected power cuts. I can easily break
> it in a well-reproducible way by doing:
> date > bar.txt && rm foo.sh
> sleep 2s
> [power cut]
> 
> On the next boot LEDE/OpenWrt script calls the same mount function but it
> results in:
> [   10.017235] overlayfs: failed to create directory /overlay/work/work (errno: 17); mounting read-only
> 
> I tracked that error and got a following forward trace for it:
> ovl_fill_super
> ovl_workdir_create
> ovl_cleanup
> vfs_rmdir
> ubifs_rmdir
> check_dir_empty
> 
> In other words mounting overlayfs fails because ubifs refuses to remove
> work/work as this directory is not empty. On a clean boot /overlay/work/work is
> empty and everything works fine but after a power cut I can see
> /overlay/work/work/#c752f2a8 file.
> 
> I don't really know anything about overlayfs and its workdir, I just expected
> overlayfs to recover from such situation on its own. FWIW after a power cut and
> reboot my bar.txt is an empty file and foo.sh still exists.
> 
> Does it sound like an overlayfs issue to you? Can you think of some way of
> fixing this?

overlayfs does not issue a recursive rm on workdir, AFAICT you are supposed to cleanup
workdir yourself before mounting.
Miklos?

Thanks,
//richard