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

Paul E. McKenney
2020-05-05T22:24:31Z

On Wed, May 06, 2020 at 12:05:04AM +0200, Thomas Gleixner wrote:
> "Paul E. McKenney" <paulmck@kernel.org> writes:
>
> > On Tue, May 05, 2020 at 03:44:05PM +0200, Thomas Gleixner wrote:
> >> 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.
> >>
> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> >> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> >> Cc: Joel Fernandes <joel@joelfernandes.org>
> >
> > The ->dynticks_nmi_nesting field is going away at some point, but
> > there is always "git merge". ;-)
>
> Yes. The logistics for merging all of this is going to be interesting :)

;-) ;-) ;-)

Thanx, Paul