linux-kernel - Re: [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race

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Date:   Wed, 26 Jun 2019 10:59:11 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 1/3] module: Fix livepatch/ftrace module text
 permissions race

On Wed, 26 Jun 2019 16:44:45 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> > 
> > It should be enough to fix the original problem because
> > x86 is the only architecture that calls set_all_modules_text_rw()
> > in ftrace path and supports livepatching at the same time.  
> 
> Looks correct, but I've paged out all the gory details vs. lock ordering in
> that area.

I don't believe ftrace_lock and text_mutex had an order before Petr's
initial patches. Reversing them shouldn't be an issue here. They were
basically both "leaf" mutexes (not grabbing any mutexes when they are
held).

-- Steve