Re: [PATCH 1/9] cpu: Introduce clear_tasks_mm_cpumask() helper

On Thu, Apr 26, 2012 at 04:59:11PM -0700, Andrew Morton wrote: [...]

...

so its not like new tasks will ever get this cpu set in

• * their mm mask. -- Peter Zijlstra
  

• * Thus, we may use rcu_read_lock() here, instead of grabbing
  

• * full-fledged tasklist_lock.
  

• */
  

• rcu_read_lock();
• for_each_process(p) {

• struct task_struct *t;
  

• t = find_lock_task_mm(p);
  

• if (!t)
  

• 	continue;
  

• cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
  

• task_unlock(t);
  

• }
• rcu_read_unlock();

+}

It is good that this code exists under CONFIG_HOTPLUG_CPU. Did you check that everything works correctly with CONFIG_HOTPLUG_CPU=n?

Yeah, only the code under CONFIG_HOTPLUG_CPU calls the function, so it should be all fine.

Thanks!