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    Subject[RFC PATCH v4 7/9] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly
    Date
    Once stop_machine() is gone from the CPU offline path, we won't be able to
    depend on local_irq_save() to prevent CPUs from going offline from under us.

    Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline,
    while invoking from atomic context.

    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    kernel/sched/core.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index cff7656..4b982bf 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -4312,6 +4312,7 @@ bool __sched yield_to(struct task_struct *p, bool preempt)
    unsigned long flags;
    bool yielded = 0;

    + get_online_cpus_atomic();
    local_irq_save(flags);
    rq = this_rq();

    @@ -4339,13 +4340,14 @@ again:
    * Make p's CPU reschedule; pick_next_entity takes care of
    * fairness.
    */
    - if (preempt && rq != p_rq)
    + if (preempt && rq != p_rq && cpu_online(task_cpu(p)))
    resched_task(p_rq->curr);
    }

    out:
    double_rq_unlock(rq, p_rq);
    local_irq_restore(flags);
    + put_online_cpus_atomic();

    if (yielded)
    schedule();


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