linux-kernel - Re: [PATCH v2] tracing/perf: Move rcu_irq_enter/exit

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Message-ID: <20200211111828.48058768@gandalf.local.home>
Date:   Tue, 11 Feb 2020 11:18:28 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH v2] tracing/perf: Move rcu_irq_enter/exit_irqson() to
 perf trace point hook

On Tue, 11 Feb 2020 16:34:52 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> > +		if (unlikely(in_nmi()))
> > +			goto out;  
> 
> unless I'm mistaken, we can simply do rcu_nmi_enter() in this case, and
> rcu_nmi_exit() on the other end.
> 
> > +		rcu_irq_enter_irqson();

The thing is, I don't think this can ever happen. We've had in the
tracepoint.h:

		/* srcu can't be used from NMI */			\
		WARN_ON_ONCE(rcuidle && in_nmi());			\

And this has yet to trigger.

-- Steve