Messages in this thread | | | Date | Wed, 6 Jun 2018 09:57:08 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle injection framework |
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On 05-06-18, 16:54, Daniel Lezcano wrote: > On 05/06/2018 12:39, Viresh Kumar wrote: > I don't think you are doing a mistake. Even if this can happen > theoretically, I don't think practically that is the case. > > The play_idle() has 1ms minimum sleep time. > > The scenario you are describing means: > > 1. the loop in idle_injection_wakeup() takes more than 1ms to achieve
There are many ways in which idle_injection_wakeup() can get called.
- from hrtimer handler, this happens in softirq context, right? So interrupts can still block the handler to run ?
- from idle_injection_start(), process context. RT or DL or IRQ activity can block the CPU for long durations sometimes.
> 2. at the same time, the user of the idle injection unregisters while > the idle injection is acting precisely at CPU0 and exits before another > task was wakeup by the loop in 1. more than 1ms after. > > >From my POV, this scenario can't happen.
Maybe something else needs to be buggy as well to make this crap happen.
> Anyway, we must write rock solid code
That's my point.
> so may be we can use a refcount to > protect against that, so instead of freeing in unregister, we refput the > ii_dev pointer.
I think the solution can be a simple change in implementation of idle_injection_wakeup(), something like this..
+static void idle_injection_wakeup(struct idle_injection_device *ii_dev) +{ + struct idle_injection_thread *iit; + int cpu; + + for_each_cpu_and(cpu, ii_dev->cpumask, cpu_online_mask) + atomic_inc(&ii_dev->count); + + mb(); //I am not sure but I think we need some kind of barrier here ? + + for_each_cpu_and(cpu, ii_dev->cpumask, cpu_online_mask) { + iit = per_cpu_ptr(&idle_injection_thread, cpu); + iit->should_run = 1; + wake_up_process(iit->tsk); + } +}
-- viresh
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