linux-kernel - Re: [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump optimization

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Message-Id: <1259183331.21397.71.camel@gandalf.stny.rr.com>
Date:	Wed, 25 Nov 2009 16:08:51 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	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>
Subject: Re: [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump
 optimization

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


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