linux-kernel - Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting

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Message-ID: <4FC7BC1D.8030002@zytor.com>
Date:	Thu, 31 May 2012 11:44:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Dave Jones <davej@...hat.com>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting

On 05/30/2012 06:28 PM, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> When the NMI handler runs, it checks if it preempted a debug
> handler and if that handler is using the debug stack. If it is, it
> changes the IDT table not to update the stack, otherwise it will
> reset the debug stack and corrupt the debug handler it preempted.
> 
> Now that ftrace uses breakpoints to change functions from nops to 
> callers, many more places may hit a breakpoint. Unfortunately this 
> includes some of the calls that lockdep performs. Which causes
> issues with the debug stack. It too needs to change the debug stack
> before tracing (if called from the debug handler).
> 
> Allow the debug_stack_set_zero() and debug_stack_reset() to be
> nested so that the debug handlers can take advantage of them too.
> 

NAK on this in its current form.  A few minutes to let me write up a
technical review.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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