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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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