On Thu, Feb 13, 2020 at 05:51:38AM -0800, Paul E. McKenney wrote: > The reason for the irq argument is to avoid invoking > rcu_prepare_for_idle() and rcu_dynticks_task_enter() from NMI context > from rcu_nmi_exit_common(). Similarly, we need to avoid invoking > rcu_dynticks_task_exit() and rcu_cleanup_after_idle() from NMI context > from rcu_nmi_enter_common(). Aaah, I see. I didn't grep hard enough earlier today (I only found stubs). Yes, those take locks, we mustn't call them from NMI context. > It might well be that I could make these functions be NMI-safe, but > rcu_prepare_for_idle() in particular would be a bit ugly at best. > So, before looking into that, I have a question. Given these proposed > changes, will rcu_nmi_exit_common() and rcu_nmi_enter_common() be able > to just use in_nmi()? That _should_ already be the case today. That is, if we end up in a tracer and in_nmi() is unreliable we're already screwed anyway.
