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    SubjectRe: [PATCH 09/14] xen/pvticketlock: Xen implementation for PV ticket locks
    On 11/17/2010 12:11 AM, Jan Beulich wrote:
    >>>> On 16.11.10 at 22:08, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
    >> +static void xen_lock_spinning(struct arch_spinlock *lock, unsigned want)
    >> {
    >> - struct xen_spinlock *xl = (struct xen_spinlock *)lock;
    >> - struct xen_spinlock *prev;
    >> int irq = __get_cpu_var(lock_kicker_irq);
    >> - int ret;
    >> + struct xen_lock_waiting *w = &__get_cpu_var(lock_waiting);
    >> + int cpu = smp_processor_id();
    >> u64 start;
    >>
    >> /* If kicker interrupts not initialized yet, just spin */
    >> if (irq == -1)
    >> - return 0;
    >> + return;
    >>
    >> start = spin_time_start();
    >>
    >> - /* announce we're spinning */
    >> - prev = spinning_lock(xl);
    >> + w->want = want;
    >> + w->lock = lock;
    >> +
    >> + /* This uses set_bit, which atomic and therefore a barrier */
    >> + cpumask_set_cpu(cpu, &waiting_cpus);
    > Since you don't allow nesting, don't you need to disable
    > interrupts before you touch per-CPU state?

    Yes, I think you're right - interrupts need to be disabled for the bulk
    of this function.

    J


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