Comment 0 for bug 1359514

Issue: CPU affinity is changed while irqbalance is running.

    + Problem explanation:

      - Old code

        + Call xgene_msi_cascade function (CPU x)

        + raw_spin_lock(&desc->lock); (CPU x)

        + Goto generic_handle_irq (CPU x)

        + The CPU x doesn't have a chance to exit the xgene_msi_cascade function to unlock desc->lock before Linux scheduce and call xgene_msi_set_affinity (irqbalance is caller) in the same CPU x

        + In irq_set_affinity, call raw_spin_lock_irqsave(&desc->lock, flags) which cause deadlock to CPU x because it disables preempt

      - New code

        + Use chained_irq_enter and exit as the standard way to cascade interrupt functions.