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    SubjectRe: [PATCH 3/6] cgroup: introduce cgroup_taskset and use it in subsys->can_attach(), cancel_attach() and attach()
    On Thu, 25 Aug 2011 10:40:06 +0200
    Tejun Heo <> wrote:

    > Hello,
    > On Thu, Aug 25, 2011 at 10:21 AM, KAMEZAWA Hiroyuki
    > <> wrote:
    > >> Hmmm... the above is basically identity transformation of the existing
    > >> code.  If the above is broken, the current code is broken too.  Is it?
    > >>
    > > Current code is not broken.
    > Trust me. If the posted code is broken, the current code is too. It
    > is an IDENTITY transformation.
    > > mem_cgroup_can_attach(....., task) need to do real job only when task->mm->owner
    > > == task. In this modification, you pass a set of task at once.
    > Before the change, cgroup would migrate multiple tasks all the same
    > but memcg wouldn't have noticed it unless it opted in explicitly using
    > [can_]attach_task(). When multiple tasks were moving, [can_]attach()
    > would only be called with the leader whether the leader actually is
    > changing cgroup or not. The interface sucked and it wasn't properly
    > documented but that's what was happening. The interface change is just
    > making the breakage obvious - +1 for the new interface. :)
    Thank you for clarification. Ok, current code is broken.

    > > So, mem_cgroup_can_attach() need to check _all_ tasks in tset rather than a
    > > first task in tset. please scan and find mm->owner.
    > >
    > > Anyway, if you merge this onto mm-tree first, I think I can have time to
    > > write a fix up if complicated.
    > As for specific merging order, it shouldn't matter all that much but
    > if you wanna backport fixes for -stable, maybe it would make more
    > sense to sequence the fix before this change.
    > Thank you.

    Sure. IIUC, the case thread_leader != mm->owner is uncommon.
    I'll consider a fix onto your fix, first.

    I'll cosinder a fix for stable tree if someone requests.


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