linux-kernel - Re: [PATCH] kprobes: Fix to delay the kprobes jump optimization

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Date:   Fri, 19 Feb 2021 11:47:44 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Uladzislau Rezki <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Michal Hocko <mhocko@...e.com>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH] kprobes: Fix to delay the kprobes jump optimization

On Fri, Feb 19, 2021 at 02:36:07PM -0500, Steven Rostedt wrote:
> On Thu, 18 Feb 2021 23:29:23 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > Commit 36dadef23fcc ("kprobes: Init kprobes in early_initcall")
> > moved the kprobe setup in early_initcall(), which includes kprobe
> > jump optimization.
> > The kprobes jump optimizer involves synchronize_rcu_tasks() which
> > depends on the ksoftirqd and rcu_spawn_tasks_*(). However, since
> > those are setup in core_initcall(), kprobes jump optimizer can not
> > run at the early_initcall().
> > 
> > To avoid this issue, make the kprobe optimization disabled in the
> > early_initcall() and enables it in subsys_initcall().
> > 
> > Note that non-optimized kprobes is still available after
> > early_initcall(). Only jump optimization is delayed.
> > 
> > Fixes: 36dadef23fcc ("kprobes: Init kprobes in early_initcall")
> > Reported-by: Paul E. McKenney <paulmck@...nel.org>
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > Cc: stable@...r.kernel.org
> > ---
> 
> I pulled this into my queue to be tested, and when that completes
> (hopefully without failure), I'll add this to my pull request for the
> current merge window (which I still need to send).

Thank you, Steve!

Could you please add the following Reported-by tags?

Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Reported-by: Uladzislau Rezki <urezki@...il.com>

Sebastian first noticed the problem, and Uladzislau figured out
how softirqs were involved.

						Thanx, Paul