Re: PATCH: Fix race in cpu_down (hotplug cpu)

Srivatsa Vaddagiri
2005-09-19T06:24:18Z

On Mon, Sep 19, 2005 at 04:11:11PM +1000, Nigel Cunningham wrote:
> > Ok, that makes sense. Nigel, could you confirm which idle routine you are
> > using?
>
> >From dmesg:
>
> monitor/mwait feature present.
> using mwait in idle threads.

Ok, that may explain why __cpu_die is timing out for you! Can you try a
(untested, I am afraid) patch on these lines:

--- process.c.org 2005-09-19 11:44:57.000000000 +0530
+++ process.c 2005-09-19 11:48:28.000000000 +0530
@@ -245,16 +245,18 @@ EXPORT_SYMBOL_GPL(cpu_idle_wait);
*/
static void mwait_idle(void)
{
+ int cpu = raw_smp_processor_id();
+
local_irq_enable();

if (!need_resched()) {
set_thread_flag(TIF_POLLING_NRFLAG);
do {
__monitor((void *)&current_thread_info()->flags, 0, 0);
- if (need_resched())
+ if (need_resched() || cpu_is_offline(cpu))
break;
__mwait(0, 0);
- } while (!need_resched());
+ } while (!need_resched() || !cpu_is_offline(cpu));
clear_thread_flag(TIF_POLLING_NRFLAG);
}
}

Other idle routines will need similar fix.

> Ok, but what about default_idle?

default_idle should be fine as it is. IOW it should not cause __cpu_die to
timeout.

--

Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017