Hello,
I believe the 4.4.y kernel has broken overlayfs: removing the file
which is present in lower layer, then renaming a file from upper layer
to have the same name fails with ESTALE. This pattern is used quite
often, for example by 'depmod' and 'apt-get update'. The bug only seems
to happen when some of the underlying directories are on tmpfs.
The test script (below) works fine on Ubuntu kernel 4.4.0-34-generic or
earlier, and it fails in Ubuntu kernel 4.4.0-36-generic. This
corresponds to Linux 4.4.16.
The error is:
mv: cannot move 'ovf/file.new' to 'ovf/file': Stale file handle
While I have not performed the full bisect, there were only 3 patches
touching 'fs/overlayfs' which went into the tree between the two revisions:
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/xenial/log/?id=b275624b3b4303d21eefd78c5b3bf04c34267e4e
ovl: verify upper dentry before unlink and rename
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/xenial/commit/?id=a4452ab01db4780937d4e19861d3b841c373c3b5
ovl: verify upper dentry in ovl_remove_and_whiteout()
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/xenial/commit/?id=90089541cf2982cff69724c34f7ae9a088df9c2f
ovl: Copy up underlying inode's ->i_mode to overlay inode
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/xenial/commit/?id=8326f3ef42b56d97d1060adff6d4ab35818e3b9a
Of them, the first two add a return with ESTALE error and would be the
prime suspects.
I also understand that 4.4.16 is a somewhat old kernel, but I believe
the bug may still be present in the latest linux-4.4.y -- there were no
changes to the relevant file (fs/overlayfs/dir.c) since these patches.
Mikhail Afanasyev
~~~~~~~~ TEST SCRIPT ~~~~~~
#!/bin/sh -ex
mkdir -p /tmp/ovf-bug-demo
cd /tmp/ovf-bug-demo
umount ./tmpfs/ovf || true
umount ./tmpfs || true
mkdir -p tmpfs
mount -t tmpfs none tmpfs
cd tmpfs
mkdir -p upper lower ovf work
touch lower/file
mount -t overlayfs none -o
rw,noatime,lowerdir=$PWD/lower,upperdir=$PWD/upper,workdir=$PWD/work
$PWD/ovf
touch ovf/file.new
rm ovf/file
mv ovf/file.new ovf/file
~~~~~~~~~ END ~~~~~~~~~~~~
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