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    SubjectRe: [PATCH V2 16/19] csky: SMP support
    On Mon, Jul 02, 2018 at 01:30:19AM +0800, Guo Ren wrote:
    > +static irqreturn_t handle_ipi(int irq, void *dev)
    > +{
    > + unsigned long *pending_ipis = &ipi_data[smp_processor_id()].bits;
    > +
    > + while (true) {
    > + unsigned long ops;
    > +
    > + /* Order bit clearing and data access. */
    > + mb();
    > +
    > + ops = xchg(pending_ipis, 0);
    > + if (ops == 0)
    > + return IRQ_HANDLED;
    > +
    > + if (ops & (1 << IPI_RESCHEDULE))
    > + scheduler_ipi();
    > +
    > + if (ops & (1 << IPI_CALL_FUNC))
    > + generic_smp_call_function_interrupt();
    > +
    > + BUG_ON((ops >> IPI_MAX) != 0);
    > +
    > + /* Order data access and bit testing. */
    > + mb();
    > + }
    > +
    > + return IRQ_HANDLED;
    > +}
    > +
    > +static void (*send_arch_ipi)(const unsigned long *mask, unsigned long irq) = NULL;
    > +
    > +void __init set_send_ipi(void (*func)(const unsigned long *, unsigned long))
    > +{
    > + if (send_arch_ipi)
    > + return;
    > +
    > + send_arch_ipi = func;
    > +}
    > +
    > +static void
    > +send_ipi_message(const struct cpumask *to_whom, enum ipi_message_type operation)
    > +{
    > + int i;
    > +
    > + mb();
    > + for_each_cpu(i, to_whom)
    > + set_bit(operation, &ipi_data[i].bits);
    > +
    > + mb();
    > + send_arch_ipi(cpumask_bits(to_whom), IPI_IRQ);
    > +}


    Please explain those mb()'s... I'm thinking you meant to use smp_mb().

    But then for handle_ipi(), the xchg() should already imply all those.
    And the send_ipi_message() only needs the second.

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