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    SubjectRe: [PATCH 09/14] xen/pvticketlock: Xen implementation for PV ticket locks
    >>> 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?

    Jan



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