[SRU][Xenial][PATCH v2 0/2]
daniel.axtens at canonical.com
Wed Nov 8 06:41:49 UTC 2017
A user is seeing failures from extracting tar archives on overlay
filesystems on the 4.4 kernel in constrained environments. The error
`tar: ./deps/0/bin: Directory renamed before its status could be extracted`
Following this thread
(https://www.spinics.net/lists/linux-unionfs/msg00856.html), it appears
that this occurs when entries in the kernel's inode cache are
reclaimed, and subsequent lookups return new inode numbers.
Further testing showed that when setting
`/proc/sys/vm/vfs_cache_pressure` to 0 (don't allow the kernel to
reclaim inode cache entries due to memory pressure) the error does not
recur, supporting the hypothesis that cache entries are being
evicted. However, this setting may lead to a kernel OOM so is not a
reasonable workaround even temporarily.
The error cannot be reproduced on a 4.13 kernel, due to the series at
particular relevant commit is
b7a807dc2010334e62e0afd89d6f7a8913eb14ff, which needs a dependency.
Backport the key commit and the dependency.
# Testing this bug
The testcase for this particular bug is simple - create an overlay
filesystem with all layers on the same underlying file system, and
then see if the inode of a directory is constant across dropping the
mkdir -p /upper/upper /upper/work /lower
mount -t overlay none /mnt -o lowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work
stat a # observe inode number
echo 2 > /proc/sys/vm/drop_caches
stat a # compare inode number
If the inode number is the same, the fix is successful.
# Regression testing
I have run the unionmount test suite from
overlay mode (./run --ov), and verified that it still passes.
(The series cover letter mentions a fork of the test suite at
have *not* attempted to get this running: it assumes a range of
changes that are not present in our kernels.)
As this changes overlayfs, there is potential for regression in the
form of unexpected breakages to overlaysfs behaviour.
I think this is adequately addressed by the regression testing.
v2: drop patches that are not strpctly required
minor change to patch 2 to not rely on ORIGIN type, as in Xenial
Amir Goldstein (2):
ovl: check if all layers are on the same fs
ovl: persistent inode number for directories
fs/overlayfs/dir.c | 36 ++++++++++++++++++++++++++++++++----
fs/overlayfs/overlayfs.h | 1 +
fs/overlayfs/ovl_entry.h | 2 ++
fs/overlayfs/super.c | 8 ++++++++
fs/overlayfs/util.c | 7 +++++++
5 files changed, 50 insertions(+), 4 deletions(-)
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