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Date:   Sun, 10 Jul 2022 11:42:42 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Tao Zhou <tao.zhou@linux.dev>
Cc:     Daniel Bristot de Oliveira <bristot@kernel.org>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Jonathan Corbet <corbet@lwn.net>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Marco Elver <elver@google.com>,
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        "Paul E. McKenney" <paulmck@kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Gabriele Paoloni <gpaoloni@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Clark Williams <williams@redhat.com>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH V4 01/20] rv: Add Runtime Verification (RV) interface
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On Sun, 10 Jul 2022 23:11:43 +0800
Tao Zhou <tao.zhou@linux.dev> wrote:

> The @*pos of enable_monitors_start() can not be -1 or other negative value.
> And I checked that the *pos is 0(right?). That is safe. Sorry for not being
> that ture and maybe this is a notice here. Because if it is a negative value,
> the returned m_def is a point to a data place 16 bytes before &rv_monitors_list.
> That is a not ture rv_monitors_list stucture data. But it is not possiable now.
> Maybe "inspired" from your question. Look it more, I image this simulation.
> If the monitor(and all is enabled) is more enough to let the *pos to increase
> to -1. And the returned m_def is last monitor that returned from enable_monitors_start().
> The enable_monitors_next() check from the last monitor and return NULL.
> Only show the last monitor. This will not really happen I think.
> But I am not focus enough to the seq file code or others now, so this may be
> more possible to be not right. Late reply continued from me..


So basically you are saying we should have:

> +static void *enabled_monitors_start(struct seq_file *m, loff_t *pos)
> +{
> +       struct rv_monitor_def *m_def;
> +       loff_t l;
> +
> +       mutex_lock(&rv_interface_lock);

	if (list_empty(&rv_monitors_list->list))
		return NULL;
?

Probably safer to have that.

-- Steve


> +       m_def = list_entry(&rv_monitors_list, struct rv_monitor_def, list);
> +
> +       for (l = 0; l <= *pos; ) {
> +               m_def = enabled_monitors_next(m, m_def, &l);
> +               if (!m_def)
> +                       break;
> +       }
> +
> +       return m_def;
> +}