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Date: Sat, 13 May 2017 00:15:03 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Steven Rostedt <rostedt@goodmis.org>
cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [RFC][PATCH 2/5] cpu-hotplug: Allow get_online_cpus() to nest
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References: <20170512171544.100715273@goodmis.org> <20170512172450.000006488@goodmis.org>
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On Fri, 12 May 2017, Steven Rostedt wrote:
>  void get_online_cpus(void)
>  {
> +#ifdef CONFIG_LOCKDEP
> +	if (current->goc_depth++)
> +		return;

This must be unconditional and not depend on lockdep. The percpu rwsem is
going to deadlock silently otherwise when a writer is waiting ....

Thanks,

	tglx