linux-kernel - Re: [PATCH -tip V4 3/4] kprobes: Fix to protect kick_kprobe_optimizer() by kprobe

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Date:   Tue, 3 Mar 2020 18:52:36 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>, paulmck@...nel.org,
        joel@...lfernandes.org,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip V4 3/4] kprobes: Fix to protect
 kick_kprobe_optimizer() by kprobe_mutex

On Wed, 26 Feb 2020 17:59:51 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> In kprobe_optimizer() kick_kprobe_optimizer() is called
> without kprobe_mutex, but this can race with other caller
> which is protected by kprobe_mutex.
> 
> To fix that, expand kprobe_mutex protected area to protect
> kick_kprobe_optimizer() call.
> 

Should we add

 Cc: stable@...r.kernel.org
 Fixes: cd7ebe2298ff ("kprobes: Use text_poke_smp_batch for optimizing")

tags?

-- Steve

> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  kernel/kprobes.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 38d9a5d7c8a4..6d76a6e3e1a5 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -592,11 +592,12 @@ static void kprobe_optimizer(struct work_struct *work)
>  	mutex_unlock(&module_mutex);
>  	mutex_unlock(&text_mutex);
>  	cpus_read_unlock();
> -	mutex_unlock(&kprobe_mutex);
>  
>  	/* Step 5: Kick optimizer again if needed */
>  	if (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list))
>  		kick_kprobe_optimizer();
> +
> +	mutex_unlock(&kprobe_mutex);
>  }
>  
>  /* Wait for completing optimization and unoptimization */