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Date: Wed, 4 Oct 2017 12:41:01 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: mingo@redhat.com, x86@kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Alexei Starovoitov <ast@kernel.org>, Alexei Starovoitov <ast@fb.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [BUGFIX PATCH] kprobes/x86: Remove IRQ disabling from jprobe
 handlers
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* Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Hmm, actually we can not disable jprobe, that has no separate Kconfig.
> So we need to introduce new kconfig for that.
> 
> And, there are several network protocols using jprobe to trace events.
> (e.g. NET_DCCPPROBE and NET_TCPPROBE)
> I think they need to migrate to trace-event at first.
> 
> So, how about below idea?
> 
> 1. Introduce CONFIG_JPROBE_API which only separate jprobe general parts
>      (no arch dependent code involves) and make it default n.
> 2. Mark break_handler and jprobe APIs deprecated so that no new user comes up.
> 3. migrate in-kernel jprobe user to trace-event or ftrace.
>    (may take some time)

So my suggestion would be to just return from register_jprobe() and don't register 
anything. Yes, there are usecases of jprobes in the kernel, but they all look 
pretty ancient and unused.

So let's try this for -next and see whether anyone has a real usecase. And no 
Kconfig and deprecation messages - those don't really work in practice - just 
disable the functionality and force people to (trivially) modify the source if 
they want to re-enable it.

If this is fine for a single release then we can just remove it all:

> 4. after that, we can completely remove jprobe which will be a series for
>    all archs. (or just one big patch?)

we want a series of patches - but that's for later.

Thanks,

	Ingo