linux-kernel - Re: [PATCH v3] kprobes: Disable Kprobe when ftrace arming fails

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Date:	Mon, 23 Mar 2015 11:33:27 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Ananth NMavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] kprobes: Disable Kprobe when ftrace arming fails


* Petr Mladek <pmladek@...e.cz> wrote:

> On Mon 2015-03-23 09:54:26, Ingo Molnar wrote:
> > 
> > * Petr Mladek <pmladek@...e.cz> wrote:
> > 
> > > arm_kprobe_ftrace() could fail, especially after introducing ftrace 
> > > IPMODIFY flag and LifePatching. But this situation is not properly 
> > > handled.
> > 
> > s/LifePatching/LivePatching?
> 
> Great catch! This is well hidden typo. Please, find the fixed version
> below.
> 
> 
> > Why not fix live patching to still allow kprobes that worked before?
> 
> Yup, Kretprobes would work out of box. Masami is working on removing
> the conflict there.
> 
> Jprobes are doable but the solution would be rather complicated. 
> LivePatching would need to tell Jprobe the right address where to 
> continue (according to the universe). We currently solve this by

wth is a 'universe' in this context?

> the conflict. I am not sure if a better solution is worth the effort.
> IMHO, LivePatch users won't want to have Kprobes on a production
> system all the time. They could use Kprobe or attach Jprobe to the
> new version of the function when needed.

So please outline the current usage limitations, why those limitations 
are in place and how you see they should be fixed/addressed.

> Below is the patch with the fixed typo.

So the typo is totally immaterial compared to the above fundamental 
patch-coordination problems between live patching, ftrace and kprobes 
...

Thanks,

	Ingo
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