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    SubjectRe: [PATCH 04/40] sched: implement __set_cpus_allowed()
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    On Wed, 2010-01-20 at 17:35 +0900, Tejun Heo wrote:
    > Hello,
    >
    > On 01/19/2010 05:37 PM, Peter Zijlstra wrote:
    > > On Tue, 2010-01-19 at 10:07 +0900, Tejun Heo wrote:
    > >>
    > >> It's also necessary to guarantee forward progress during CPU_DOWN.
    > >> The problem with kthread_bind() is that it's not synchronized against
    > >> CPU hotplug operations. It needs outer synchronization like calling
    > >> it directly from CPU_DOWN_PREP. I guess it's doable but I think it
    > >> would be better to simply share the backend implementation between
    > >> set_cpus_allowed_ptr() and kthread_bind().
    > >
    > > OK, so you're saying you need to migrate the rescue thread during
    > > cpu-down. That thread is guaranteed sleeping right,
    >
    > No, it's not. It might have been tasked to process works from other
    > CPUs.

    OK, so maybe I'm confused, but in general the workqueue thing needs to
    ensure work affinity, right? So why can we move the rescue thread while
    its processing another CPU's works?



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