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    SubjectRe: [PATCH 1/2] workqueue: Move wq_update_unbound_numa() to the beginning of CPU_ONLINE
    On Tue, Jun 21, 2016 at 07:42:31PM +0530, Gautham R Shenoy wrote:
    > > Subject: [PATCH] sched: allow kthreads to fallback to online && !active cpus
    > >
    > > During CPU hotplug, CPU_ONLINE callbacks are run while the CPU is
    > > online but not active. A CPU_ONLINE callback may create or bind a
    > > kthread so that its cpus_allowed mask only allows the CPU which is
    > > being brought online. The kthread may start executing before the CPU
    > > is made active and can end up in select_fallback_rq().
    > >
    > > In such cases, the expected behavior is selecting the CPU which is
    > > coming online; however, because select_fallback_rq() only chooses from
    > > active CPUs, it determines that the task doesn't have any viable CPU
    > > in its allowed mask and ends up overriding it to cpu_possible_mask.
    > >
    > > CPU_ONLINE callbacks should be able to put kthreads on the CPU which
    > > is coming online. Update select_fallback_rq() so that it follows
    > > cpu_online() rather than cpu_active() for kthreads.
    > >
    > > Signed-off-by: Tejun Heo <tj@kernel.org>
    > > Reported-by: Gautham R Shenoy <ego@linux.vnet.ibm.com>
    >
    > Hi Tejun,
    >
    > This patch fixes the issue on POWER. I am able to see the worker
    > threads of the unbound workqueues of the newly onlined node with this.
    >
    > Tested-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>

    Peter?

    --
    tejun

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