linux-kernel - Re: [PATCH 0/3] livepatch/rcu: Handle some subtle issues between livepatching and RCU

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Message-Id: <20170504165521.GA3956@linux.vnet.ibm.com>
Date:   Thu, 4 May 2017 09:55:21 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, Jessica Yu <jeyu@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Steven Rostedt <rostedt@...dmis.org>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] livepatch/rcu: Handle some subtle issues between
 livepatching and RCU

On Thu, May 04, 2017 at 12:55:13PM +0200, Petr Mladek wrote:
> Steven and Paul recently discussed some issues when using RCU
> functionality in ftrace handlers. A good summary can be found at
> https://lkml.kernel.org/r/20170412115304.3077dbc8@gandalf.local.home
> 
> This discussion made us to revisit the ftrace handler used by
> the livepatches. Some changes seem to be needed. A perfect solution
> looks rather complicated. I have implemented a sub-optimal
> one and split it into three patches for easier review.
> 
> Please, note that we were on the safe side before introducing
> the hybrid consistency model. The ftrace handler worked correctly
> with empty function stack. Also the patch removal was not possible.
> But we need to be more careful now.

I don't know enough to say much about the live patching, but the
characterization of how RCU works is correct.

						Thanx, Paul

> Petr Mladek (3):
>   livepatch/rcu: Guarantee consistency when patching idle kthreads
>   livepatch/rcu: Warn when system consistency is broken in RCU code
>   livepatch/rcu: Disable livepatch removal when safety is not guaranteed
> 
>  Documentation/livepatch/livepatch.txt | 19 +++++++++++++++++++
>  kernel/livepatch/patch.c              | 14 ++++++++++++++
>  kernel/livepatch/transition.c         |  7 ++++++-
>  kernel/livepatch/transition.h         |  2 ++
>  4 files changed, 41 insertions(+), 1 deletion(-)
> 
> -- 
> 1.8.5.6
>