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

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 11/17/2010 12:11 AM, Jan Beulich wrote:
>>>> 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?

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

    J

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