Re: [patch V4 part 3 11/29] rcu: Provide rcu_irq_exit_preempt()

Joel Fernandes
2020-05-14T02:46:55Z

On Wed, May 13, 2020 at 10:41:16PM -0400, Joel Fernandes wrote:
> Hi Thomas,
>
> On Tue, May 05, 2020 at 03:44:05PM +0200, Thomas Gleixner wrote:
>
> Thank you for CC'ing me.
>
> > Interrupts and exceptions invoke rcu_irq_enter() on entry and need to
> > invoke rcu_irq_exit() before they either return to the interrupted code or
> > invoke the scheduler due to preemption.
> >
> > The general assumption is that RCU idle code has to have preemption
> > disabled so that a return from interrupt cannot schedule. So the return
> > from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq().
> >
> > If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code
> > had preemption enabled then this goes unnoticed until the CPU goes idle or
> > some other RCU check is executed.
> >
> > Provide rcu_irq_exit_preempt() which can be invoked from the
> > interrupt/exception return code in case that preemption is enabled. It
> > invokes rcu_irq_exit() and contains a few sanity checks in case that
> > CONFIG_PROVE_RCU is enabled to catch such issues directly.
>
> Could you let me know which patch or part in the multi-part series is using it?

Ah I see its "x86/entry/common: Provide idtentry_enter/exit()" patch. I'll go
read that tomorrow. Thanks!

- Joel