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

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Date:   Fri, 19 Feb 2021 14:36:07 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Paul E . McKenney" <paulmck@...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 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).

Thanks!

-- Steve