group.of.nepali.translators team mailing list archive

[Launchpad Bug Tracker <1839521@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package zfs-linux - 0.6.5.6-0ubuntu28

---------------
zfs-linux (0.6.5.6-0ubuntu28) xenial; urgency=medium

  * Fix ZFS shrinker deadlock with xattrs (LP: #1839521)
    - Upstream ZFS fix 31b6111fd92a ("Kill zp->z_xattr_parent to prevent pinning")
      and ddae16a9cf0b ("xattr dir doesn't get purged during iput") fix a deadlock
      in shrinker path when a xattr directory inode and its xattr inode are in the
      same disposal list and the xattr dir inode is evicted before the xattr inode.

 -- Mauricio Faria de Oliveira <mfo@xxxxxxxxxxxxx>  Wed, 07 Aug 2019
11:01:11 -0300

** Changed in: zfs-linux (Ubuntu Xenial)
       Status: Fix Committed => Fix Released

-- 
You received this bug notification because you are a member of नेपाली
भाषा समायोजकहरुको समूह, which is subscribed to Xenial.
Matching subscriptions: Ubuntu 16.04 Bugs
https://bugs.launchpad.net/bugs/1839521

Title:
  Xenial: ZFS deadlock in shrinker path with xattrs

Status in zfs-linux package in Ubuntu:
  Fix Released
Status in zfs-linux source package in Xenial:
  Fix Released

Bug description:
  [Impact]

   * Xenial's ZFS can deadlock in the memory shrinker path
     after removing files with extended attributes (xattr).

   * Extended attributes are enabled by default, but are
     _not_ used by default, which reduces the likelyhood.

   * It's very difficult/rare to reproduce this problem,
     due to file/xattr/remove/shrinker/lru order/timing
     circumstances required. (weeks for a reporter user)
     but a synthetic test-case has been found for tests.

  [Test Case]

   * A synthetic reproducer is available for this LP,
     with a few steps to touch/setfattr/rm/drop_caches
     plus a kernel module to massage the disposal list.
     (comment #8)

   * In the original ZFS module:
     the xattr dir inode is not purged immediately on
     file removal, but possibly purged _two_ shrinker
     invocations later.  This allows for other thread
     started before file remove to call zfs_zget() on
     the xattr child inode and iput() it, so it makes
     to the same disposal list as the xattr dir inode.
     (comment #3)

   * In the modified ZFS module:
     the xattr dir inode is purged immediately on file
     removal not possibly later on shrinker invocation,
     so the problem window above doesn't exist anymore.
     (comment #12)

  [Regression Potential]

   * Low. The patches are confined to extended attributes
     in ZFS, specifically node removal/purge, and another
     change how an xattr child inode tracks its xattr dir
     (parent) inode, so that it can be purged immediately
     on removal.

   * The ZFS test-suite has been run on original/modified
     zfs-dkms package/kernel modules, with no regressions.
     (comment #11)

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/1839521/+subscriptions