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    Subject[PATCH v6 21/46] block: 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 preempt_disable() or local_irq_disable() 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: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    block/blk-softirq.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/block/blk-softirq.c b/block/blk-softirq.c
    index 467c8de..448f9a9 100644
    --- a/block/blk-softirq.c
    +++ b/block/blk-softirq.c
    @@ -58,6 +58,8 @@ static void trigger_softirq(void *data)
    */
    static int raise_blk_irq(int cpu, struct request *rq)
    {
    + get_online_cpus_atomic();
    +
    if (cpu_online(cpu)) {
    struct call_single_data *data = &rq->csd;

    @@ -66,9 +68,11 @@ static int raise_blk_irq(int cpu, struct request *rq)
    data->flags = 0;

    __smp_call_function_single(cpu, data, 0);
    + put_online_cpus_atomic();
    return 0;
    }

    + put_online_cpus_atomic();
    return 1;
    }
    #else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */


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