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    Subject[PATCH v2 23/45] infiniband: ehca: Use get/put_online_cpus_atomic() to prevent CPU offline
    Date
    Once stop_machine() is gone from the CPU offline path, we won't be able
    to depend on disabling preemption 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.

    Cc: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
    Cc: Christoph Raisch <raisch@de.ibm.com>
    Cc: Roland Dreier <roland@kernel.org>
    Cc: Sean Hefty <sean.hefty@intel.com>
    Cc: Hal Rosenstock <hal.rosenstock@gmail.com>
    Cc: linux-rdma@vger.kernel.org
    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    drivers/infiniband/hw/ehca/ehca_irq.c | 5 +++++
    1 file changed, 5 insertions(+)

    diff --git a/drivers/infiniband/hw/ehca/ehca_irq.c b/drivers/infiniband/hw/ehca/ehca_irq.c
    index 8615d7c..ace901e 100644
    --- a/drivers/infiniband/hw/ehca/ehca_irq.c
    +++ b/drivers/infiniband/hw/ehca/ehca_irq.c
    @@ -43,6 +43,7 @@

    #include <linux/slab.h>
    #include <linux/smpboot.h>
    +#include <linux/cpu.h>

    #include "ehca_classes.h"
    #include "ehca_irq.h"
    @@ -703,6 +704,7 @@ static void queue_comp_task(struct ehca_cq *__cq)
    int cq_jobs;
    unsigned long flags;

    + get_online_cpus_atomic();
    cpu_id = find_next_online_cpu(pool);
    BUG_ON(!cpu_online(cpu_id));

    @@ -720,6 +722,7 @@ static void queue_comp_task(struct ehca_cq *__cq)
    BUG_ON(!cct || !thread);
    }
    __queue_comp_task(__cq, cct, thread);
    + put_online_cpus_atomic();
    }

    static void run_comp_task(struct ehca_cpu_comp_task *cct)
    @@ -759,6 +762,7 @@ static void comp_task_park(unsigned int cpu)
    list_splice_init(&cct->cq_list, &list);
    spin_unlock_irq(&cct->task_lock);

    + get_online_cpus_atomic();
    cpu = find_next_online_cpu(pool);
    target = per_cpu_ptr(pool->cpu_comp_tasks, cpu);
    thread = *per_cpu_ptr(pool->cpu_comp_threads, cpu);
    @@ -768,6 +772,7 @@ static void comp_task_park(unsigned int cpu)
    __queue_comp_task(cq, target, thread);
    }
    spin_unlock_irq(&target->task_lock);
    + put_online_cpus_atomic();
    }

    static void comp_task_stop(unsigned int cpu, bool online)


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