Date: Tue, 24 Nov 2009 08:52:49 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>,
       Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
       lkml <linux-kernel@vger.kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
       Jim Keniston <jkenisto@us.ibm.com>,
       Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
       Christoph Hellwig <hch@infradead.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Anders Kaseorg <andersk@ksplice.com>, Tim Abbott <tabbott@ksplice.com>,
       Andi Kleen <andi@firstfloor.org>, Jason Baron <jbaron@redhat.com>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       systemtap <systemtap@sources.redhat.com>,
       DLE <dle-develop@lists.sourceforge.net>
Subject: Re: [PATCH -tip v5 00/10] kprobes: Kprobes jump optimization support
Message-ID: <20091124075249.GC21991@elte.hu>
References: <20091123232115.22071.71558.stgit@dhcp-100-2-132.bos.redhat.com>
 <20091124020315.GA6221@nowhere>
 <20091124032008.GD6752@nowhere>
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* Frederic Weisbecker <fweisbec@gmail.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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