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List:       linux-fsdevel
Subject:    Can't rmdir an empty directory when using overlayfs
From:       Francis Moreau <francis.moro () gmail ! com>
Date:       2014-08-28 14:22:11
Message-ID: 53FF3B13.3060103 () gmail ! com
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Hello,

I've a weird problem when using overlayfs.

The version I'm using is quite old, it's v12 on top of a 3.4 kernel. I
guess the patches are coming from:


http://git.kernel.org/cgit/linux/kernel/git/apw/overlayfs.git/log/?h=overlayfs.v12apw1

Sorry if the version is old but I'm stick with 3.4 and v12 seems the
latest version available for this kernel.

My problem is that I can't rmdir an empty directory, it fails with
'device or resource busy'.

This directory is created by an application and is used to mount a block
device. Once the job is finished the block device is unmounted and
finally app tries to rmdir it.

The directory doesn't seem to be a mountpoint (anymore). Looking in
/proc/mounts confirm this.

I tried to trace what's going on in the kernel when calling the syscall
'rmdir' and found that it's currently failing in vfs_rmdir() when
testing for that particular condition:

 error = -EBUSY;
 if (d_mountpoint(dentry))
         goto out;

If I'm not mistaken, the kernel still thinks that the directory is a
mountpoint.

Another weird behaviour is that if I'm touching/modifying some unrelated
files (not in the directory) before starting my app, then the issue
disappear.

Does this issue seem to be an old known issue ?

Thanks !
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