linux-kernel - Re: [LKP] [sched] BUG: kernel boot hang

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Message-ID: <20150216133447.50135132@gandalf.local.home>
Date:	Mon, 16 Feb 2015 13:34:47 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Huang Ying <ying.huang@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, LKP ML <lkp@...org>
Subject: Re: [LKP] [sched] BUG: kernel boot hang

On Mon, 16 Feb 2015 19:22:38 +0100
Frederic Weisbecker <fweisbec@...il.com> wrote:
 
> Huang Ying hasn't yet reported a Tested-by but I could reproduce (with both function and function_graph tracers btw)
> and the patch fixed it.

Ah right, it's not the recursion from the function tracer that kills
us, it's the recursion from the preempt_enable_notrace() that does...

preempt_schedule_common()
  --> traced
     preempt_disable_notrace();
     preempt_enable_notrace();
     (see's NEED_RESCHED set)
	preempt_schedule_context();
	    preempt_schedule_common();
		--> traced

etc, etc till boom.

-- Steve

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