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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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