On Tue, 2011-06-07 at 11:42 -0700, H. Peter Anvin wrote:
> On 06/07/2011 11:38 AM, Suresh Siddha wrote:
> >
> > This is kind of a false positive. We are just checking if the calling
> > cpu is online/offline (and there is no possible process migration
> > between an online and offline cpu).
> >
>
> Is the state not available in a percpu variable of some sort? If not,
> shouldn't it be rather than indirecting via a CPU number?
This is what I first thought about but the current percpu cpu_state is
arch specific and not all architectures define it.
Thinking a bit more, I should be able to use the stop machine's percpu
thread state and use it here. Something like the appended. I am testing
and will send the modified patches shortly.
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index c78b0c2..97a1770 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -153,7 +153,7 @@ static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
*/
int __stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
- int online = cpu_online(smp_processor_id());
+ int online = percpu_read(cpu_stopper.enabled);
int include_this_offline = 0;
struct cpu_stop_work *work;
struct cpu_stop_done done;
@@ -513,13 +513,13 @@ int __stop_machine(int (*fn)(void *), void *data, const
struct cpumask *cpus)
.active_cpus = cpus };
/* Include the calling cpu that might not be online yet. */
- if (!cpu_online(smp_processor_id()))
+ if (!percpu_read(cpu_stopper.enabled))
smdata.num_threads++;
/* Set the initial state and stop all online cpus. */
set_state(&smdata, STOPMACHINE_PREPARE);
- if (cpu_online(smp_processor_id()))
+ if (percpu_read(cpu_stopper.enabled))
return stop_cpus(cpu_online_mask, stop_machine_cpu_stop,
&smdata);
else
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