linux-kernel - Re: [PATCH V7 01/16] rv: Add Runtime Verification (RV) interface

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Date:   Thu, 28 Jul 2022 00:10:10 +0800
From:   Tao Zhou <tao.zhou@...ux.dev>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Gabriele Paoloni <gpaoloni@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-trace-devel@...r.kernel.org, Tao Zhou <tao.zhou@...ux.dev>
Subject: Re: [PATCH V7 01/16] rv: Add Runtime Verification (RV) interface

On Mon, Jul 25, 2022 at 10:11:13PM +0200, Daniel Bristot de Oliveira wrote:

> +void rv_put_task_monitor_slot(int slot)
> +{
> +	lockdep_assert_held(&rv_interface_lock);
> +
> +	if (slot < 0 || slot >= RV_PER_TASK_MONITORS) {
> +		WARN_ONCE(1, "RV releasing an invalid slot!: %d\n", slot);
> +		return;
> +	}
> +
> +	WARN_ONCE(!task_monitor_slots[slot], "RV releasing unused task_monitor_slots: %d\n",
> +		  slot);
> +
> +	task_monitor_count--;
> +	task_monitor_slots[slot] = false;
> +}

I would say this can be implemented using bits. Also is an optimization.
But now here just use bool and seems not that needed.

> +static void turn_monitoring_off(void)
> +{
> +	WRITE_ONCE(monitoring_on, false);
> +	/* monitoring_on */
> +	smp_wmb();

Absolutely the sync I can not see.
If not store another after smp_wmb(), even you have smp_wmb() pair,
it is not valid in my poor mind that there is no another load before
loading of monitoring_on that ensure something like if the another
load is *what* then the after load is ensured to be *what* statement
(I am sure I am poor on these, but just some words input yeah).