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Date: Mon, 23 Mar 2015 11:33:27 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Petr Mladek <pmladek@suse.cz>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        "David S. Miller" <davem@davemloft.net>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        Ananth NMavinakayanahalli <ananth@in.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        Jiri Kosina <jkosina@suse.cz>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] kprobes: Disable Kprobe when ftrace arming fails
Message-ID: <20150323103327.GA12213@gmail.com>
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 <20150323101253.GN11869@pathway.suse.cz>
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* Petr Mladek <pmladek@suse.cz> wrote:

> On Mon 2015-03-23 09:54:26, Ingo Molnar wrote:
> > 
> > * Petr Mladek <pmladek@suse.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