On 06/26/2013 07:09 PM, Ralf Baechle wrote:
> On Wed, Jun 26, 2013 at 02:02:57AM +0530, Srivatsa S. Bhat wrote:
>
>> Once stop_machine() is gone from the CPU offline path, we won't be able
>> to depend on disabling preemption to prevent CPUs from going offline
>> from under us.
>>
>> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
>> offline, while invoking from atomic context.
>
> I think the same change also needs to be applied to r4k_on_each_cpu() in
> arch/mips/mm/c-r4k.c which currently looks like:
>
> static inline void r4k_on_each_cpu(void (*func) (void *info), void *info)
> {
> preempt_disable();
>
> #if !defined(CONFIG_MIPS_MT_SMP) && !defined(CONFIG_MIPS_MT_SMTC)
> smp_call_function(func, info, 1);
> #endif
> func(info);
> preempt_enable();
> }
>
Thanks for pointing this out! I'll include changes to this code in my
next version.
Regards,
Srivatsa S. Bhat
> This is a slightly specialized version of on_each_cpu() which only calls
> out to other CPUs in actual multi-core environments and also - unlike
> on_each_cpu() doesn't disable interrupts for the sake of better
> interrupt latencies.
>
> Which reminds me ...
>
> Andrew, I was wondering why did 78eef01b0fae087c5fadbd85dd4fe2918c3a015f
> [[PATCH] on_each_cpu(): disable local interrupts] disable interrupts?
> The log is:
>
> ----- snip -----
> When on_each_cpu() runs the callback on other CPUs, it runs with local
> interrupts disabled. So we should run the function with local interrupts
> disabled on this CPU, too.
>
> And do the same for UP, so the callback is run in the same environment on bo
> UP and SMP. (strictly it should do preempt_disable() too, but I think
> local_irq_disable is sufficiently equivalent).
> [...]
> ----- snip -----
>
> I'm not entirely convinced the symmetry between UP and SMP environments is
> really worth it. Would anybody mind removing the local_irq_disable() ...
> local_irq_enable() from on_each_cpu()?
>
