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SubjectRe: [PATCH 01/27] smpboot: Provide a generic method to boot secondary processors
On 06/03/2012 02:23 PM, Yong Zhang wrote:

> On Fri, Jun 01, 2012 at 05:39:27PM +0530, Srivatsa S. Bhat wrote:
>> +void __cpuinit smpboot_start_secondary(void *arg)
>> +{
>> + unsigned int cpu;
>> +
>> + /*
>> + * SMP booting is extremely fragile in some architectures. So run
>> + * the cpu initialization code first before anything else.
>> + */
>> + __cpu_pre_starting(arg);
>> +
>> + preempt_disable();
>> + cpu = smp_processor_id();
>> +
>> + /* Invoke the CPU_STARTING notifier callbacks */
>> + notify_cpu_starting(cpu);
>> +
>> + __cpu_pre_online(arg);
>> +
>> + /* Set the CPU in the cpu_online_mask */
>> + set_cpu_online(cpu, true);
>> +
>> + __cpu_post_online(arg);
>> +
>
> Seems it worth to catch incorrect irq state here:
>
> WARN_ON_ONCE(!irqs_disabled());
>


That's a good point! But unfortunately we can't do that just yet.
Because, some architectures have explicit comments that say that
irqs must be enabled at a certain point in time, or have something
special than just a local_irq_enable(), and hence fall under the
__cpu_post_online() function when converted to this model.

Examples: ARM (patch 26) and ia64 (patch 15)

Unless the maintainers give a go-ahead to change them, I don't
think it would be safe.. (I have added the Notes section to each
patch to get the attention of the maintainers to such issues).

Regards,
Srivatsa S. Bhat

>
>> + /* Enable local interrupts now */
>> + local_irq_enable();
>> +
>> + wmb();
>> + cpu_idle();
>> +
>> + /* We should never reach here! */
>> + BUG();
>> +}




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