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Date:   Sun, 10 Jul 2022 23:11:43 +0800
From:   Tao Zhou <tao.zhou@linux.dev>
To:     Daniel Bristot de Oliveira <bristot@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.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>,
        Dmitry Vyukov <dvyukov@google.com>,
        "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, Tao Zhou <tao.zhou@linux.dev>
Subject: Re: [PATCH V4 01/20] rv: Add Runtime Verification (RV) interface
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On Fri, Jul 08, 2022 at 04:39:47PM +0200,
Daniel Bristot de Oliveira wrote:

> Hey Tao!
> 
> On 7/6/22 19:49, Tao Zhou wrote:
> >> +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);
> >> +	m_def = list_entry(&rv_monitors_list, struct rv_monitor_def, list);
> > I realized this m_def is not real but vain. Is it possible the loop is
> > skiped and just return m_def that is not valid.
> 
> that is empty... not a problem.
> 
> I am not seeing (the possible) problem here. Could you simulate/reproduce the problem?

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..

Thanks,
Tao