linux-kernel - Re: [PATCH] livepatch/rcu: Fix stacking of patches when RCU infrastructure is patched

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Date:   Tue, 23 May 2017 12:52:47 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jessica Yu <jeyu@...hat.com>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] livepatch/rcu: Fix stacking of patches when RCU
 infrastructure is patched

On Tue, May 23, 2017 at 05:47:31PM +0200, Petr Mladek wrote:
> diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
> index f8269036bf0b..08acba30ecec 100644
> --- a/kernel/livepatch/patch.c
> +++ b/kernel/livepatch/patch.c
> @@ -59,7 +59,11 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>  
>  	ops = container_of(fops, struct klp_ops, fops);
>  
> -	rcu_read_lock();
> +	/*
> +	 * A variant of synchronize_sched() is used to allow pathing functions
> +	 * where RCU is not wathing, see klp_synchronize_transition().
> +	 */
> +	preempt_disable_notrace();

s/pathing/patching/
s/wathing/watching/

(and same for the duplicated version of the comment below.)

Otherwise the patch looks promising, though I'll need to stare at it for
a while...

-- 
Josh