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Date:   Wed, 06 May 2020 00:05:04 +0200
From:   Thomas Gleixner <>
Cc:     LKML <>,,
        Andy Lutomirski <>,
        Alexandre Chartre <>,
        Frederic Weisbecker <>,
        Paolo Bonzini <>,
        Sean Christopherson <>,
        Masami Hiramatsu <>,
        Petr Mladek <>,
        Steven Rostedt <>,
        Joel Fernandes <>,
        Boris Ostrovsky <>,
        Juergen Gross <>,
        Brian Gerst <>,
        Mathieu Desnoyers <>,
        Josh Poimboeuf <>,
        Will Deacon <>
Subject: Re: [patch V4 part 3 11/29] rcu: Provide rcu_irq_exit_preempt()

"Paul E. McKenney" <> 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 <>
>> Cc: "Paul E. McKenney" <>
>> Cc: Joel Fernandes <>
> 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 :)

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