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Message-ID: <20190712111125.GT3402@hirez.programming.kicks-ass.net>
Date: Fri, 12 Jul 2019 13:11:25 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc: linux-kernel@...r.kernel.org,
Alexey Kuznetsov <kuznet@....inr.ac.ru>,
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"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader
checking
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();
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