linux-kernel - Re: [PATCH v4 07/27] rcu: Make RCU IRQ enter/exit functions rely on in

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Date:   Wed, 26 Feb 2020 01:23:21 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        rostedt@...dmis.org, mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, dan.carpenter@...cle.com,
        mhiramat@...nel.org
Subject: Re: [PATCH v4 07/27] rcu: Make RCU IRQ enter/exit functions rely on
 in_nmi()

On Fri, Feb 21, 2020 at 02:34:23PM +0100, Peter Zijlstra wrote:
> From: Paul E. McKenney <paulmck@...nel.org>
> 
> The rcu_nmi_enter_common() and rcu_nmi_exit_common() functions take an
> "irq" parameter that indicates whether these functions are invoked from
> an irq handler (irq==true) or an NMI handler (irq==false).  However,
> recent changes have applied notrace to a few critical functions such
> that rcu_nmi_enter_common() and rcu_nmi_exit_common() many now rely
> on in_nmi().  Note that in_nmi() works no differently than before,
> but rather that tracing is now prohibited in code regions where in_nmi()
> would incorrectly report NMI state.
> 
> This commit therefore removes the "irq" parameter and inlines
> rcu_nmi_enter_common() and rcu_nmi_exit_common() into rcu_nmi_enter()
> and rcu_nmi_exit(), respectively.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>

Although in the end, from a naming POV, it would make more sense to have
rcu_nmi_enter() calling rcu_irq_enter() rather than the opposite. But the
result would be another level of function in the way to keep the
NOKPROBE property, so I guess we'll stick with that layout.