linux-kernel - Re: [PATCH] rcu: Allow rcu_irq_enter_check

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Message-ID: <87a6vhz034.fsf@nanos.tec.linutronix.de>
Date:   Mon, 16 Nov 2020 18:24:31 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>
Cc:     eupm90@...il.com, linux-kernel@...r.kernel.org, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] rcu: Allow rcu_irq_enter_check_tick() from NMI

On Mon, Nov 16 2020 at 13:10, Peter Zijlstra wrote:

> Any which way around; here's a proper patch...
>
> ---
>
> Subject: rcu: Allow rcu_irq_enter_check_tick() from NMI
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Mon Nov 16 12:54:56 CET 2020
>
> Eugenio managed to tickle #PF from NMI context which resulted in
> hitting a WARN in RCU through irqentry_enter() ->
> __rcu_irq_enter_check_tick().
>
> However, this situation is perfectly sane and does not warrant an
> WARN. The #PF will (necessarily) be atomic and not require messing
> with the tick state, so early return is correct.
>
> Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()")
> Reported-by: "Eugenio Pérez" <eupm90@...il.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Andy Lutomirski <luto@...nel.org>
> Reviewed-by: Paul E. McKenney <paulmck@...nel.org>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>