group.of.nepali.translators team mailing list archive

[Mauricio Faria de Oliveira <mfo@xxxxxxxxxxxxx>]

Public bug reported:

[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.

 * 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.

 * 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.

[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.

** Affects: zfs-linux (Ubuntu)
     Importance: Undecided
         Status: Invalid

** Affects: zfs-linux (Ubuntu Xenial)
     Importance: Undecided
     Assignee: Mauricio Faria de Oliveira (mfo)
         Status: In Progress

** Affects: zfs-linux (Ubuntu Bionic)
     Importance: Undecided
         Status: Invalid

** Affects: zfs-linux (Ubuntu Disco)
     Importance: Undecided
         Status: Invalid

** Affects: zfs-linux (Ubuntu Eoan)
     Importance: Undecided
         Status: Invalid

** Also affects: zfs-linux (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Also affects: zfs-linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Also affects: zfs-linux (Ubuntu Eoan)
   Importance: Undecided
       Status: New

** Also affects: zfs-linux (Ubuntu Disco)
   Importance: Undecided
       Status: New

** Changed in: zfs-linux (Ubuntu Eoan)
       Status: New => Invalid

** Changed in: zfs-linux (Ubuntu Disco)
       Status: New => Invalid

** Changed in: zfs-linux (Ubuntu Bionic)
       Status: New => Invalid

** Changed in: zfs-linux (Ubuntu Xenial)
       Status: New => In Progress

** Changed in: zfs-linux (Ubuntu Xenial)
     Assignee: (unassigned) => Mauricio Faria de Oliveira (mfo)

-- 
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:
  Invalid
Status in zfs-linux source package in Xenial:
  In Progress
Status in zfs-linux source package in Bionic:
  Invalid
Status in zfs-linux source package in Disco:
  Invalid
Status in zfs-linux source package in Eoan:
  Invalid

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.

   * 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.

   * 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.

  [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.

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