linux-kernel - Re: Oops caused by race between livepatch and ftrace

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Date:   Wed, 29 May 2019 13:17:21 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Johannes Erdfelt <johannes@...felt.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Ingo Molnar <mingo@...hat.com>, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Oops caused by race between livepatch and ftrace

On Tue, 21 May 2019, Steven Rostedt wrote:

> > Hm.  I suppose using ftrace_lock might be less risky since that lock 
> > is only used internally by ftrace (up until now).  But I think it 
> > would also make less sense because the text_mutex is supposed to 
> > protect code patching.  And presumably ftrace_lock is supposed to be 
> > ftrace-specific.
> > 
> > Here's the latest patch, still using text_mutex.  I added some lockdep
> > assertions to ensure the permissions toggling functions are always
> > called with text_mutex.  It's running through 0-day right now.  I can
> > try to run it through various tests with CONFIG_LOCKDEP.
> 
> Yeah, text_mutex probably does make more sense. ftrace_mutex was around
> before text_mutex as ftrace was the first one to do the runtime
> patching (after boot has finished). It wasn't until we introduced
> text_poke that we decided to create the text_mutex locking as well.
> 
> > 
> > 
> > From: Josh Poimboeuf <jpoimboe@...hat.com>
> > Subject: [PATCH] livepatch: Fix ftrace module text permissions race
> 
> Thanks,
> 
> I'll try to find some time to test this as well.

Steve, Jessica, any final word on this?

Thanks,

-- 
Jiri Kosina
SUSE Labs