[PATCH v2 2/6] genirq: Allow an interrupt to be marked as 'raw'

Valentin Schneider valentin.schneider at arm.com
Sat Dec 5 14:24:15 EST 2020

On 03/12/20 15:52, Valentin Schneider wrote:
> On 03/12/20 13:03, Peter Zijlstra wrote:
>> The scheduler IPI really doesn't need RCU either ;-)
> But as with any other interrupt, we could then go through:
>   preempt_schedule_irq() ~> pick_next_task_fair() -> newidle_balance()
> which does enter a read-side section, so RCU would need to be
> watching. Looking at kernel/entry/common.c:irqentry_exit_cond_resched(), it
> seems we do check for this via rcu_irq_exit_check_preempt().
> I however cannot grok why irqentry_exit() *doesn't* call into
> preempt_schedule_irq() if RCU wasn't watching on IRQ entry

RCU wasn't watching on IRQ entry:
  -> we should be on the idle task
  -> no unvoluntary preemption for the idle task, scheduling always happens
     at the tail of the idle loop
  -> ignore what I've been saying, current patch is fine

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