linux-kernel - Re: [PATCH -tip v4 3/3] kprobes: Support delayed unoptimization

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Message-ID: <20101126072621.GB19589@elte.hu>
Date:	Fri, 26 Nov 2010 08:26:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, 2nddept-manager@....hitachi.co.jp,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH -tip v4 3/3] kprobes: Support delayed unoptimization


* Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> Unoptimization occurs when a probe is unregistered or disabled, and
> is heavy because it recovers instructions by using stop_machine().
> This patch delays unoptimization operations and unoptimize several
> probes at once by using text_poke_smp_batch().
> This can avoid unexpected system slowdown coming from stop_machine().
> 
> Changes in v2:
> - Use dynamic allocated buffers and params.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: x86@...nel.org
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> ---
> 
>  arch/x86/include/asm/kprobes.h |    4 
>  arch/x86/kernel/kprobes.c      |   45 ++++
>  include/linux/kprobes.h        |    2 
>  kernel/kprobes.c               |  434 +++++++++++++++++++++++++++-------------
>  4 files changed, 344 insertions(+), 141 deletions(-)

Hm, this is a scary big patch with non-trivial effects - it should be broken up as 
much as possible, into successive, bisectable steps. The end result looks mostly 
fine - it's just this one huge step of a patch that is dangerous.

Thanks,

	Ingo
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