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From:   Thomas Gleixner <tglx@linutronix.de>
To:     paulmck@kernel.org
Cc:     LKML <linux-kernel@vger.kernel.org>, rcu@vger.kernel.org,
        Andrew Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH x86/entry: Force rcu_irq_enter() when in idle task
In-Reply-To: <20200612191921.GA18255@paulmck-ThinkPad-P72>
References: <20200611235305.GA32342@paulmck-ThinkPad-P72> <CALCETrWo-zpiDsYGtKvm8LzW6CQ5L19a3+Ag_9g8aL4wHaJj9g@mail.gmail.com> <871rmkzcc8.fsf@nanos.tec.linutronix.de> <87wo4cxubv.fsf@nanos.tec.linutronix.de> <20200612174953.GA19188@paulmck-ThinkPad-P72> <20200612191921.GA18255@paulmck-ThinkPad-P72>
Date:   Fri, 12 Jun 2020 21:25:20 +0200
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"Paul E. McKenney" <paulmck@kernel.org> writes:
> On Fri, Jun 12, 2020 at 10:49:53AM -0700, Paul E. McKenney wrote:
>> I will therefore address this issue in a follow-on patch.
>
> I should add that -your- patch from yesterday did -not- cause this
> problem, in case that is of interest.

So I still can add it back and amend the changelog and comment:

Change the condition from !rcu_is_watching() to is_idle_task(current) ||
rcu_is_watching() which enforces that interrupts in the idle task
unconditionally invoke rcu_irq_enter() independent of the RCU state. For
most scenarios is_idle_task() would be sufficient but Task RCU needs it
according to Paul.

Thanks,

        tglx