Public bug reported: [SRU Justification]
[Impact] A user is seeing failures from extracting tar archives on overlay filesystems on the 4.4 kernel in constrained environments. The error presents as: `tar: ./deps/0/bin: Directory renamed before its status could be extracted` Following this thread (http://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 https://www.spinics.net/lists/linux-fsdevel/msg110235.html. The particular relevant commit is b7a807dc2010334e62e0afd89d6f7a8913eb14ff, which needs a couple of dependencies. [Fix] For Zesty, backport the entire series. For Xenial, where a full backport is not feasible, backport the key commit and the short list of dependencies. [Testcase] # 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 caches: mkdir -p /upper/upper /upper/work /lower mount -t overlay none /mnt -o lowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work cd /mnt mkdir a 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 http://git.infradead.org/users/dhowells/unionmount-testsuite.git in overlay mode (./run --ov), and verified that it still passes. (The series cover letter mentions a fork of the test suite at https://github.com/amir73il/unionmount-testsuite/commits/overlayfs- devel. I have *not* attempted to get this running: it assumes a range of changes that are not present in our kernels.) [Regression Potential] 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. One option to reduce the regression potential on Zesty is to reduce the set of patches applied - rather than including the whole series we could include just the patches to solve this bug, which are much easier to inspect for correctness. ** Affects: linux (Ubuntu) Importance: Undecided Assignee: Daniel Axtens (daxtens) Status: Confirmed -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1728489 Title: tar -x sometimes fails on overlayfs To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1728489/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
