linux-kernel - Re: [PATCH 2/2] x86: Make the x86-64 stacktrace code safely callable from scheduler

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Message-ID: <20110512204051.GD7410@nowhere>
Date:	Thu, 12 May 2011 22:40:54 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/2] x86: Make the x86-64 stacktrace code safely
 callable from scheduler

On Thu, May 12, 2011 at 10:32:06PM +0200, Frederic Weisbecker wrote:
> Avoid potential scheduler recursion and deadlock from the
> stacktrace code by avoiding rescheduling when we re-enable
> preemption.
> 
> This robustifies some scheduler trace events like sched switch
> when they are used to produce callchains in perf or ftrace.

Actually trace events are already safe because they already disable
preemption so callchains won't call schedule() there. But still
let's be careful, we never know how stacktrace can be used.
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