linux-kernel - Re: [PATCH 2/2] ftrace: Adjust priority of ftrace module notifier

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Date:	Fri, 29 Jan 2016 09:38:00 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jessica Yu <jeyu@...hat.com>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Ingo Molnar <mingo@...hat.com>, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ftrace: Adjust priority of ftrace module notifier

On Fri, 29 Jan 2016 01:43:47 -0500
Jessica Yu <jeyu@...hat.com> wrote:


> ---
>  kernel/trace/ftrace.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index eca592f..bdd7bfc 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5067,7 +5067,12 @@ static int ftrace_module_notify(struct notifier_block *self,
>  
>  struct notifier_block ftrace_module_nb = {
>  	.notifier_call = ftrace_module_notify,
> -	.priority = INT_MIN,	/* Run after anything that can remove kprobes */
> +	/*
> +	 * Run after anything that can remove kprobes and
> +	 * after livepatch's going notifier, but run before
> +	 * livepatch's coming notifier.
> +	 */
> +	.priority = INT_MIN+1,
>  };
>  
>  void __init ftrace_init(void)

Actually, I rather break up the ftrace notifiers into two different
notifiers. One for coming and one for going (I use to have that before
hard coding the module updates in the module code).

Have the coming notifier be INT_MAX, where it runs before everything
else (which it should, as tracing should be enabled then). And have the
module going to stay INT_MIN to run after everything.

-- Steve