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Date:   Fri, 12 Jul 2019 13:11:25 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Bjorn Helgaas <bhelgaas@google.com>,
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
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        kernel-hardening@lists.openwall.com,
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        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
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        Pavel Machek <pavel@ucw.cz>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
        rcu@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Tejun Heo <tj@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, will@kernel.org,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>
Subject: Re: [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader
 checking
Message-ID: <20190712111125.GT3402@hirez.programming.kicks-ass.net>
References: <20190711234401.220336-1-joel@joelfernandes.org>
 <20190711234401.220336-2-joel@joelfernandes.org>
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On Thu, Jul 11, 2019 at 07:43:56PM -0400, Joel Fernandes (Google) wrote:
> +int rcu_read_lock_any_held(void)
> +{
> +	int lockdep_opinion = 0;
> +
> +	if (!debug_lockdep_rcu_enabled())
> +		return 1;
> +	if (!rcu_is_watching())
> +		return 0;
> +	if (!rcu_lockdep_current_cpu_online())
> +		return 0;
> +
> +	/* Preemptible RCU flavor */
> +	if (lock_is_held(&rcu_lock_map))

you forgot debug_locks here.

> +		return 1;
> +
> +	/* BH flavor */
> +	if (in_softirq() || irqs_disabled())

I'm not sure I'd put irqs_disabled() under BH, also this entire
condition is superfluous, see below.

> +		return 1;
> +
> +	/* Sched flavor */
> +	if (debug_locks)
> +		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> +	return lockdep_opinion || !preemptible();

that !preemptible() turns into:

  !(preempt_count()==0 && !irqs_disabled())

which is:

  preempt_count() != 0 || irqs_disabled()

and already includes irqs_disabled() and in_softirq().

> +}

So maybe something lke:

	if (debug_locks && (lock_is_held(&rcu_lock_map) ||
			    lock_is_held(&rcu_sched_lock_map)))
		return true;

	return !preemptible();