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

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Date:   Fri, 28 Jun 2019 01:25:13 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.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, Josh Poimboeuf wrote:
> On Fri, Jun 28, 2019 at 01:09:08AM +0200, Thomas Gleixner wrote:
> > On Thu, 27 Jun 2019, Steven Rostedt wrote:
> > > I agree with Josh on this. As the original bug was the race between
> > > ftrace and live patching / modules changing the text from ro to rw and
> > > vice versa. Just protecting the update to the text permissions is more
> > > robust, and should be more self documenting when we need to handle
> > > other architectures for this.
> > 
> > How is that supposed to work?
> > 
> >     ftrace  	     	
> > 	prepare()
> > 	 setrw()
> > 			setro()
> > 	patch <- FAIL
> 
> /me dodges frozen shark
> 
> You are right of course.  My brain has apparently already shut off for
> the day.
> 
> Maybe a comment or two would help though.

Agreed. That would indeed be useful.

Thanks,

	tglx