Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752581AbdI2Ook (ORCPT <rfc822;w@1wt.eu>);
        Fri, 29 Sep 2017 10:44:40 -0400
Received: from mail.kernel.org ([198.145.29.99]:41358 "EHLO mail.kernel.org"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752285AbdI2Ooj (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 29 Sep 2017 10:44:39 -0400
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5E7B220BED
Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org
Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=mhiramat@kernel.org
Date: Fri, 29 Sep 2017 07:44:36 -0700
From: Masami Hiramatsu <mhiramat@kernel.org>
To: Ingo Molnar <mingo@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>
Subject: Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for
 optprobe with CONFIG_PREEMPT
Message-Id: <20170929074436.f447187d99e5e78008b15234@kernel.org>
In-Reply-To: <20170929073755.ypjz6cidn7aiyxbq@gmail.com>
References: <150581509713.32348.1905525476438163954.stgit@devbox>
        <150581537997.32348.14125457458719053753.stgit@devbox>
        <20170928072220.iv5subwl4u4zcqcp@gmail.com>
        <20170929002938.64cb852d6d921ec013d7f052@kernel.org>
        <20170929073755.ypjz6cidn7aiyxbq@gmail.com>
X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1341
Lines: 52

On Fri, 29 Sep 2017 09:37:55 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > On Thu, 28 Sep 2017 09:22:20 +0200
> > Ingo Molnar <mingo@kernel.org> wrote:
> > 
> > > 
> > > * Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > > 
> > > > To enable jump optimized probe with CONFIG_PREEMPT, use
> > > > synchronize_rcu_tasks() to wait for all tasks preempted
> > > > on trampoline code back on track.
> > > 
> > > This sentence does not parse. It's missing a verb, but I'm not sure.
> > 
> > Hmm, how about this?
> > 
> > Use synchthnize_rcu_tasks() to wait for all tasks preempted
> > on trampoline code back on track so that jump optimized probe
> > can be enabled with CONFIG_PREEMPT.
> 
> What's "synchthnize"? ...

Oops, it's my typo. my XPS touch pad is really unstable...

> 
> More seriously, I still don't understand it. What is 'back on track'?
> 
> Do you mean to say:
> 
>    We want to wait for all potentially preempted kprobes trampoline execution to 
>    have completed. This guarantees that any freed trampoline memory is not in use
>    by any task in the system anymore. synchronize_rcu_tasks() gives such a
>    guarantee, so use it.

Exactly, this is correct!

Thank you,

> 
> or something else?
> 
> Thanks,
> 
> 	Ingo


-- 
Masami Hiramatsu <mhiramat@kernel.org>