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    SubjectRe: [PATCH cgroup/for-4.4-fixes 2/3] cgroup: fix handling of multi-destination migration from subtree_control enabling
    On Mon, Nov 30, 2015 at 05:44:31PM -0500, Tejun Heo wrote:
    > From 0d7d444e260493252e30c70813c7657e9ede2f12 Mon Sep 17 00:00:00 2001
    > From: Tejun Heo <tj@kernel.org>
    > Date: Mon, 30 Nov 2015 17:24:34 -0500
    >
    > Consider the following v2 hierarchy.
    >
    > P0 (+memory) --- P1 (-memory) --- A
    > \- B
    >
    > P0 has memory enabled in its subtree_control while P1 doesn't. If
    > both A and B contain processes, they would belong to the memory css of
    > P1. Now if memory is enabled on P1's subtree_control, memory csses
    > should be created on both A and B and A's processes should be moved to
    > the former and B's processes the latter. IOW, enabling controllers
    > can cause atomic migrations into different csses.
    >
    > The core cgroup migration logic has been updated accordingly but the
    > controller migration methods haven't and still assume that all tasks
    > migrate to a single target css; furthermore, the methods were fed the
    > css in which subtree_control was updated which is the parent of the
    > target csses. pids controller depends on the migration methods to
    > move charges and this made the controller attribute charges to the
    > wrong csses often triggering the following warning by driving a
    > counter negative.

    Applying 1-2 to libata/for-4.4-fixes.

    Thanks.

    --
    tejun


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