linux-kernel - Re: [PATCH v10 07/12] task_isolation: add debug boot flag

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Message-ID: <20160302203748.GH6356@twins.programming.kicks-ass.net>
Date:	Wed, 2 Mar 2016 21:37:48 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Gilad Ben Yossef <giladb@...hip.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Andy Lutomirski <luto@...capital.net>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v10 07/12] task_isolation: add debug boot flag

On Wed, Mar 02, 2016 at 03:09:31PM -0500, Chris Metcalf wrote:
> +void task_isolation_debug(int cpu)
> +{
> +	struct task_struct *p;
> +
> +	if (!task_isolation_possible(cpu))
> +		return;
> +
> +	rcu_read_lock();
> +	p = cpu_curr(cpu);
> +	get_task_struct(p);

As I think Oleg keeps reminding me, this is not actually a safe thing to
do.

> +	rcu_read_unlock();
> +	task_isolation_debug_task(cpu, p);
> +	put_task_struct(p);
> +}