* Srivatsa Vaddagiri <[EMAIL PROTECTED]> wrote:
> flush_workqueue() <- One of biggest offenders of lock_cpu_hotplug() to date
> for_each_online_cpu(cpu)
> flush_cpu_workqueue
> TASK_UNINTERRUPTIBLE sleep
>
> If we don't wait for this thread from being frozen "voluntarily"
> (because it is in TASK_UNINTERRUPTIBLE sleep), then flush_workqueue is
> clearly racy wrt cpu hotplug.
ok. But the only real problem would be for_each_online_cpu() loops that
might sleep, correct? I did a quick audit and those seem to be in the
minority by a factor of 1:10.
So ... to make the audit obviously safe, how about mechanically
converting 100% of the for_each_online_cpu() loops to something like:
mask = get_each_online_cpu_mask();
for_each_cpu_mask(mask) {
...
}
put_each_online_cpu_mask(mask);
where get_each_online_cpu_mask() also does a preempt_disable()
implicitly, and put_each_online_cpu_mask() does a preempt_enable().
(Note that no locking is needed - only preemption-disabling.)
the 10% loops that _can_ schedule would trigger the __might_sleep()
atomicity test in schedule()), and those would have to be converted a
bit more cleverly, on a case by case basis. (for example a number of
them might not even have to sleep on the for_each_online_cpu() loop)
hm?
Ingo
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