linux-kernel - Re: [PATCH] ftrace: Remove possible deadlock between register_kprobe() and ftrace_run_update

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Message-ID: <alpine.DEB.2.21.1906280017000.32342@nanos.tec.linutronix.de>
Date:   Fri, 28 Jun 2019 00:17:56 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
cc:     Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>, Jessica Yu <jeyu@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Johannes Erdfelt <johannes@...felt.com>,
        Ingo Molnar <mingo@...nel.org>, mhiramat@...nel.org,
        torvalds@...ux-foundation.org
Subject: Re: [PATCH] ftrace: Remove possible deadlock between register_kprobe()
 and ftrace_run_update_code()

On Thu, 27 Jun 2019, Petr Mladek wrote:
> Fortunately, the problematic fix is needed only on x86_64. It is
> the only architecture that calls set_all_modules_text_rw()
> in ftrace path and supports livepatching at the same time.
> 
> Therefore it is enough to move text_mutex handling from the generic
> kernel/trace/ftrace.c into arch/x86/kernel/ftrace.c:
> 
>    ftrace_arch_code_modify_prepare()
>    ftrace_arch_code_modify_post_process()
> 
> This patch basically reverts the ftrace part of the problematic

  ^^^^^^^^^ Sigh

> commit 9f255b632bf12c4dd7 ("module: Fix livepatch/ftrace module
> text permissions race"). And provides x86_64 specific-fix.
> 
> Some refactoring of the ftrace code will be needed when livepatching
> is implemented for arm or nds32. These architectures call
> set_all_modules_text_rw() and use stop_machine() at the same time.
> 
> Fixes: 9f255b632bf12c4dd7 ("module: Fix livepatch/ftrace module text permissions race")
> Signed-off-by: Petr Mladek <pmladek@...e.com>

Acked-by: Thomas Gleixner <tglx@...utronix.de>