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Subject: Re: [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump  optimization
From: Steven Rostedt <rostedt@goodmis.org>
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To: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,  Ananth N Mavinakayanahalli <ananth@in.ibm.com>, lkml <linux-kernel@vger.kernel.org>, systemtap <systemtap@sources.redhat.com>, DLE <dle-develop@lists.sourceforge.net>, Jim Keniston <jkenisto@us.ibm.com>, Srikar Dronamraju <srikar@linux.vnet.ibm.com>, Christoph Hellwig <hch@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>, 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>
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Date: Wed, 25 Nov 2009 21:09:00 -0000
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On Tue, 2009-11-24 at 15:59 -0500, Masami Hiramatsu wrote:

> > I see...so the non-preemptible kernel requirement looks
> > hard to workaround :-s
> 
> It's the next challenge I think :-)
> Even though, kprobes itself still work on preemptive kernel,
> so we don't lose any functionality.

>From kstop_machine, we could search all tasks to see if any are about to
resume in the modified location. If there is, we could either

1) insert a normal kprobe
2) modify the return address of the task to jump to some trampoline to 
   finish the work and return to the code spot with a direct jump.

#2 is kind of nasty but seems like a fun thing to implement ;-)

-- Steve