[Xen-devel] Re: [PATCH 09/14] xen/pvticketlock: Xen implementation for PV ticket locks

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 16.11.10 at 22:08, Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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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