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

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Message-ID: <4B0DA1D9.2030609@redhat.com>
Date:	Wed, 25 Nov 2009 16:30:01 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	rostedt@...dmis.org
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

Steven Rostedt wrote:
> 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 ;-)

Sure, anyway, a normal kprobe is already inserted, so we also can
just wait until all tasks don't resume to the spot :-)
(that's another reason why it uses delayed work for optimization.
 we can try it again and again.)
And I think, that code will be shared with ksplice too.

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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