On Thu, 27 Jun 2019 10:24:36 -0400
Joel Fernandes <j...@joelfernandes.org> wrote:

> > What am I missing here?  
> 
> This issue I think is
> 
> (in normal process context)
> spin_lock_irqsave(rq_lock); // which disables both preemption and interrupt
>                          // but this was done in normal process context,
>                          // not from IRQ handler
> rcu_read_lock();
>           <---------- IPI comes in and sets exp_hint

How would an IPI come in here with interrupts disabled?

-- Steve

> rcu_read_unlock()
>    -> rcu_read_unlock_special
>         -> raise_softirq_irqoff
>           -> wakeup_softirq  <--- because in_interrupt returns false.  
> 
> I think the issue is in_interrupt() does not know about threaded interrupts.
> If it did, then the ksoftirqd wake up would not happen.
> 
> Did I get something wrong?

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