Re: [RFC PATCH] ARM: smp: Fix the CPU hotplug race with scheduler.

From: Santosh Shilimkar
Date: Mon Jun 20 2011 - 06:20:13 EST

On 6/20/2011 3:20 PM, Russell King - ARM Linux wrote:
On Mon, Jun 20, 2011 at 02:53:59PM +0530, Santosh Shilimkar wrote:
The current ARM CPU hotplug code suffers from couple of race conditions
in CPU online path with scheduler.
The ARM CPU hotplug code doesn't wait for hot-plugged CPU to be marked
active as part of cpu_notify() by the CPU which brought it up before
enabling interrupts.

Hmm, why not just move the set_cpu_online() call before notify_cpu_starting()
and add the wait after the set_cpu_online() ?
I think that's what patch is doing. Do you mean, calling hotplug
notifier chain immediately after CPU marked as online. Something
like below.

set_cpu_online(cpu, true);
while (!cpumask_test_cpu(smp_processor_id(), cpu_active_mask))

* Enable local interrupts.


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