linux-kernel - Re: [RFC][PATCH 3/5] kprobes: Take get_online_cpus() before taking jump_label

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Message-Id: <20170512183911.GB3956@linux.vnet.ibm.com>
Date:   Fri, 12 May 2017 11:39:11 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [RFC][PATCH 3/5] kprobes: Take get_online_cpus() before taking
 jump_label_lock()

On Fri, May 12, 2017 at 01:15:47PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> jump_label_lock() is taken under get_online_cpus(). Make sure that kprobes
> follows suit.
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

The remaining three (3/5 through 5/5) look straightforward.  #4 appears
to be the one needing the recursive get_online_cpus().

							Thanx, Paul

> ---
>  kernel/kprobes.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index d733479a10ee..57cf73aef488 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1294,13 +1294,13 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
>  	int ret = 0;
>  	struct kprobe *ap = orig_p;
> 
> -	/* For preparing optimization, jump_label_text_reserved() is called */
> -	jump_label_lock();
>  	/*
>  	 * Get online CPUs to avoid text_mutex deadlock.with stop machine,
>  	 * which is invoked by unoptimize_kprobe() in add_new_kprobe()
>  	 */
>  	get_online_cpus();
> +	/* For preparing optimization, jump_label_text_reserved() is called */
> +	jump_label_lock();
>  	mutex_lock(&text_mutex);
> 
>  	if (!kprobe_aggrprobe(orig_p)) {
> @@ -1348,8 +1348,8 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
> 
>  out:
>  	mutex_unlock(&text_mutex);
> -	put_online_cpus();
>  	jump_label_unlock();
> +	put_online_cpus();
> 
>  	if (ret == 0 && kprobe_disabled(ap) && !kprobe_disabled(p)) {
>  		ap->flags &= ~KPROBE_FLAG_DISABLED;
> -- 
> 2.10.2
> 
>