linux-kernel - Re: [PATCH v3 tip/core/rcu 1/9] rcu: Add call_rcu

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Message-ID: <20140807084921.GK19379@twins.programming.kicks-ass.net>
Date:	Thu, 7 Aug 2014 10:49:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
	mingo@...nel.org, dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
	oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v3 tip/core/rcu 1/9] rcu: Add call_rcu_tasks()

On Tue, Aug 05, 2014 at 02:55:10PM -0700, Paul E. McKenney wrote:
> +/* Check for nohz_full CPUs executing in userspace. */
> +static void check_no_hz_full_tasks(void)
> +{
> +#ifdef CONFIG_NO_HZ_FULL
> +	int cpu;
> +	struct task_struct *t;
> +
> +	for_each_online_cpu(cpu) {
> +		cond_resched();
> +		rcu_read_lock();
> +		t = rcu_dynticks_task_cur(cpu);
> +		if (t == NULL || is_idle_task(t)) {
> +			rcu_read_unlock();
> +			continue;
> +		}
> +		if (ACCESS_ONCE(t->rcu_tasks_holdout))
> +			ACCESS_ONCE(t->rcu_tasks_holdout) = 0;
> +		rcu_read_unlock();
> +	}
> +#endif /* #ifdef CONFIG_NO_HZ_FULL */
> +}

That's not hotplug safe afaict, and I've no idea if someone pointed that
out already because people refuse to trim email and I can't be arsed to
wade through pages and pages of quoting.

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