linux-kernel - Re: [PATCH -tip v5 00/10] kprobes: Kprobes jump optimization support

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Message-ID: <20091124075249.GC21991@elte.hu>
Date:	Tue, 24 Nov 2009 08:52:49 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Anders Kaseorg <andersk@...lice.com>,
	Tim Abbott <tabbott@...lice.com>,
	Andi Kleen <andi@...stfloor.org>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip v5 00/10] kprobes: Kprobes jump optimization support


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Tue, Nov 24, 2009 at 03:03:19AM +0100, Frederic Weisbecker wrote:
> > On Mon, Nov 23, 2009 at 06:21:16PM -0500, Masami Hiramatsu wrote:
> > >   When the optimized-kprobe is hit before optimization, its handler
> > >  changes IP(instruction pointer) to copied code and exits. So, the
> > >  instructions which were copied to detour buffer are executed on the detour
> > >  buffer.
> > 
> > 
> > 
> > Hm, why is it playing such hybrid game there?
> > If I understand well, we have executed int 3, executed the
> > handler and we jump back to the detour buffer?
> > 
> 
> I got it, I think. We have instructions to patch. And the above turn 
> this area into dead code, safe to patch.
> 
> But still, stop_machine() seem to make it not necessary anymore.

i think 'sending an IPI to all online CPUs' might be an adequate 
sequence to make sure patching effects have propagated. I.e. an 
smp_call_function() with a dummy function?

	Ingo
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