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    SubjectRe: [patch] sched: prevent bound kthreads from changing cpus_allowed
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    On Mon, 2008-06-09 at 13:59 -0700, Max Krasnyanskiy wrote:
    > David Rientjes wrote:
    > >> 2) Sometimes calls to kthread_bind are binding to any online cpu, such as in:
    > >>
    > >> drivers/infiniband/hw/ehca/ehca_irq.c: kthread_bind(cct->task, any_online_cpu(cpu_online_map));
    > >>
    > >> In such cases, the PF_THREAD_BOUND seems inappropriate. The caller of
    > >> kthread_bind() really doesn't seem to care where that thread is bound;
    > >> they just want it on a CPU that is still online.
    > >>
    > >
    > > This particular case is simply moving the thread to any online cpu so that
    > > it survives long enough for the subsequent kthread_stop() in
    > > destroy_comp_task(). So I don't see a problem with this instance.
    > >
    > > A caller to kthread_bind() can always remove PF_THREAD_BOUND itself upon
    > > return, but I haven't found any cases in the tree where that is currently
    > > necessary. And doing that would defeat the semantics of kthread_bind()
    > > where these threads are supposed to be bound to a specific cpu and not
    > > allowed to run on others.
    >
    > Actually I have another use case here. Above example in particular may be ok
    > but it does demonstrate the issue nicely. Which is that in some cases kthreads
    > are bound to a CPU but do not have a strict "must run here" requirement and
    > could be moved if needed.
    > For example I need an ability to move workqueue threads. Workqueue threads do
    > kthread_bind().

    Per cpu workqueues should stay on their cpu.

    What you're really looking for is a more fine grained alternative to
    flush_workqueue().



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