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[Brad Figg <brad.figg@xxxxxxxxxxxxx>]

This bug is awaiting verification that the kernel in -proposed solves
the problem. Please test the kernel and update this bug with the
results. If the problem is solved, change the tag 'verification-needed-
trusty' to 'verification-done-trusty'.

If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!


** Tags added: verification-needed-trusty

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https://bugs.launchpad.net/bugs/1466135

Title:
  nf_conntrack releases a conntrack with non-zero refcnt

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Trusty:
  Fix Committed

Bug description:
  [Impact]
  Occasionally starting new containers or creating new net namespaces may soft lockup because of improper refcounting of conntrack entires.

  In the issue that I face, I can find a kworker thread using up an
  entire core, and when I cat /proc/$pid/stack I see this:

  <ffffffffbe01e9b6>] ___preempt_schedule+0x56/0xb0
  [<ffffffffc02223e4>] nf_ct_iterate_cleanup+0x134/0x160 [nf_conntrack]
  [<ffffffffc0223dae>] nf_conntrack_cleanup_net_list+0x4e/0x170
  [nf_conntrack]
  [<ffffffffc022436d>] nf_conntrack_pernet_exit+0x4d/0x60 [nf_conntrack]
  [<ffffffffbe6040d3>] ops_exit_list.isra.1+0x53/0x60
  [<ffffffffbe6048d0>] cleanup_net+0x100/0x1d0
  [<ffffffffbe084991>] process_one_work+0x171/0x470
  [<ffffffffbe08563b>] worker_thread+0x11b/0x3a0
  [<ffffffffbe08bb82>] kthread+0xd2/0xf0
  [<ffffffffbe71757c>] ret_from_fork+0x7c/0xb0
  [<ffffffffffffffff>] 0xffffffffffffffff

  The kworker is looping forever and failing to clean up conntrack state.
  All the while, it holds the global netns lock. Given that I've bisected
  to commit e53376bef2cd97d3e3f61fdc677fb8da7d03d0da which is to do with refcounting, I suspect that borked refcounting on conntrack entries makes them impossible to properly free/destroy, which prevents this worker from cleaning up the namespace, which then goes on to prevent anything else from interacting with namespaces (add/delete/etc).

  [Test Case]
  bug 1403152 has a testcase which can occasionally hit this issue

  [Fix]
  $ git describe --contains e53376bef2cd97d3e3f61fdc677fb8da7d03d0da
  v3.14-rc3~36^2~28^2~12

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