linux-kernel - Re: [PATCH v5 1/6] kprobes: Remove dependency to the module

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Message-ID: <20200724091711.GB517988@gmail.com>
Date:   Fri, 24 Jul 2020 11:17:11 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jessica Yu <jeyu@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v5 1/6] kprobes: Remove dependency to the module_mutex


* Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> wrote:

> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -564,7 +564,7 @@ static void kprobe_optimizer(struct work_struct *work)
>  	cpus_read_lock();
>  	mutex_lock(&text_mutex);
>  	/* Lock modules while optimizing kprobes */
> -	mutex_lock(&module_mutex);
> +	lock_modules();
>  
>  	/*
>  	 * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
> @@ -589,7 +589,7 @@ static void kprobe_optimizer(struct work_struct *work)
>  	/* Step 4: Free cleaned kprobes after quiesence period */
>  	do_free_cleaned_kprobes();
>  
> -	mutex_unlock(&module_mutex);
> +	unlock_modules();
>  	mutex_unlock(&text_mutex);
>  	cpus_read_unlock();

BTW., it would be nice to expand on the comments above - exactly which 
parts of the modules code is being serialized against and why?

We already hold the text_mutex here, which should protect against most 
kprobes related activities interfering - and it's unclear (to me) 
which part of the modules code is being serialized with here, and the 
'lock modules while optimizing kprobes' comments is unhelpful. :-)

Thanks,

	Ingo