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Date: Mon, 15 Jun 2009 14:38:41 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Linus Torvalds <torvalds@linux-foundation.org>, mingo@redhat.com,
       paulus@samba.org, acme@redhat.com, linux-kernel@vger.kernel.org,
       penberg@cs.helsinki.fi, vegard.nossum@gmail.com, efault@gmx.de,
       jeremy@goop.org, npiggin@suse.de, tglx@linutronix.de,
       linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain	support
 to use NMI-safe methods
References: <20090615184858.GD6520@Krystal> <1245091917.6741.185.camel@laptop> <20090615185907.GF6520@Krystal> <1245092561.6741.205.camel@laptop> <4A369CD8.3090505@zytor.com> <20090615192720.GA9056@Krystal> <4A36A1C7.6080005@zytor.com> <20090615210119.GD24554@elte.hu> <20090615211207.GB12919@Krystal> <20090615211605.GC27100@elte.hu> <20090615213429.GD12919@Krystal>
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Mathieu Desnoyers wrote:
> 
> As the maintainer of the out-of-tree LTTng tracer, which hooks in the
> page fault handler with tracepoints, and which can build almost entirely
> as modules, I am very tempted to argue that having the nmi-code entirely
> robust wrt in-kernel page faults would be a very-nice-to-have feature.
> 

I doubt that is ever going to be reliable, due to reentrancy issues.

	-hpa