Re: [RFC 2/2] rcu: Remove ->dynticks_nmi_nesting from struct rcu_dynticks

[Steven Rostedt]

On Fri, 22 Jun 2018 06:28:43 -0700
"Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> It has been some years since I traced the code flow, but what happened
> back then is that it switches itself from an interrupt handler to not
> without actually returning from the interrupt.  This can only happen when
> interrupting a non-idle process, thankfully, and RCU's dyntick-idle code
> relies on this restriction.  If I remember correctly, the code ends up
> executing in the context of the interrupted process, but it has been some
> years, so please apply appropriate skepticism.

If irq_enter() is not paired with irq_exit() then major things will
break. Especially since that's how in_interrupt() and friends rely on to
work.

Now, perhaps rcu_irq_enter() is called elsewhere (as a git grep appears
it may be), and that rcu_irq_enter() may not be paired with
rcu_irq_exit(). But that's not anything to do with the irq_enter() and
irq_exit() routines being paired or not.

-- Steve