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Date:   Sat, 30 Jul 2022 22:08:12 +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>,
        Randy Dunlap <rdunlap@infradead.org>,
        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 V9 01/16] rv: Add Runtime Verification (RV) interface
Message-ID: <YuU7TGxm5pzmBFTx@geo.homenetwork>
References: <cover.1659052063.git.bristot@kernel.org>
 <a4bfe038f50cb047bfb343ad0e12b0e646ab308b.1659052063.git.bristot@kernel.org>
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On Fri, Jul 29, 2022 at 11:38:40AM +0200, Daniel Bristot de Oliveira wrote:

> +static int __rv_disable_monitor(struct rv_monitor_def *mdef, bool sync)
> +{
> +	lockdep_assert_held(&rv_interface_lock);
> +
> +	if (mdef->monitor->enabled) {
> +		mdef->monitor->enabled = 0;
> +		mdef->monitor->disable();

If call disable(), the @enabled is set 0 there.

> +
> +		/*
> +		 * Wait for the execution of all events to finish.
> +		 * Otherwise, the data used by the monitor could
> +		 * be inconsistent. i.e., if the monitor is re-enabled.
> +		 */
> +		if (sync)
> +			tracepoint_synchronize_unregister();
> +		return 1;

Return 0 indicate the actually disabling and successed.

> +	}
> +	return 0;

If disable a diabled monitor, return error(negative).

> +}
> +
> +/**
> + * rv_disable_monitor - disable a given runtime monitor
> + *
> + * Returns 0 on success.
> + */
> +int rv_disable_monitor(struct rv_monitor_def *mdef)
> +{
> +	__rv_disable_monitor(mdef, true);
> +	return 0;

Always return 0 here, whatever the return value of __rv_disable_monitor().
And this enforce me to look more here, see below.

> +}

> +static ssize_t enabled_monitors_write(struct file *filp, const char __user *user_buf,
> +				      size_t count, loff_t *ppos)
> +{
> +	char buff[MAX_RV_MONITOR_NAME_SIZE + 2];
> +	struct rv_monitor_def *mdef;
> +	int retval = -EINVAL;
> +	bool enable = true;
> +	char *ptr = buff;
> +	int len;
> +
> +	if (count < 1 || count > MAX_RV_MONITOR_NAME_SIZE + 1)
> +		return -EINVAL;
> +
> +	memset(buff, 0, sizeof(buff));
> +
> +	retval = simple_write_to_buffer(buff, sizeof(buff) - 1, ppos, user_buf, count);
> +	if (retval < 0)
> +		return -EFAULT;
> +
> +	ptr = strim(buff);
> +
> +	if (ptr[0] == '!') {
> +		enable = false;
> +		ptr++;
> +	}
> +
> +	len = strlen(ptr);
> +	if (!len)
> +		return count;
> +
> +	mutex_lock(&rv_interface_lock);
> +
> +	retval = -EINVAL;
> +
> +	list_for_each_entry(mdef, &rv_monitors_list, list) {
> +		if (strcmp(ptr, mdef->monitor->name) != 0)
> +			continue;
> +
> +		/*
> +		 * Monitor found!
> +		 */
> +		if (enable)
> +			retval = rv_enable_monitor(mdef);
> +		else
> +			retval = rv_disable_monitor(mdef);

About the retval here. If count == 1 and retval == 0, then
`retval = count` --> retval == 1. This retval will be returned to 
user space and dedicate that how many character read and success
If retval is 1(it is not possiable, the return value of
da_monitor_init_*() called in enable callback in rv_enable_monitor()
will be 0, so that return value check is not needed, or any other functions
called in enable callback need to check the return value then, so I checked
the WARN_ONCE() called in macro rv_attach_trace_probe() which is called in
enable callback, if the WARN_ONCE is called, it means that something go wrong.
We need to check the return value of WARN_ONCE() in enable callback), the
return value will be returned to user space but actually the error(warn) happened.
User space do not know. They treat the two kind of return value 1 the same
but one is the write count value successed and another is the write error
value returned.
In enable callback, check rv_attach_trace_probe():

static int enable_wip(void)
{
      int retval = 1;
 	  
      /* 
       * Delete the check of return value of da_monitor_init_wip()
       * because it is always 0
       */
      da_monitor_init_wip();

      retval &= rv_attach_trace_probe("wip", preempt_enable, handle_preempt_enable);
      retval &= rv_attach_trace_probe("wip", sched_waking, handle_sched_waking);
      retval &= rv_attach_trace_probe("wip", preempt_disable, handle_preempt_disable);

      /* 
       * If the retval is not 0, it mean at least one rv_attach_trace_probe()
       * is WARN_ONCE(). I am not sure that if the first WARN_ONCE() happened,
       * then return directly or at here after all rv_attach_trace_probe() is
       * called and check the retval is 0 or 1.
       */
      if (retval)
             return -1;
      return retval;
}

> +
> +		if (!retval)
> +			retval = count;
> +
> +		break;
> +	}

> +/**
> + * rv_register_monitor - register a rv monitor.
> + * @monitor:    The rv_monitor to be registered.
> + *
> + * Returns 0 if successful, error otherwise.
> + */
> +int rv_register_monitor(struct rv_monitor *monitor)
> +{
> +	struct rv_monitor_def *r;
> +	int retval = 0;
> +
> +	if (strlen(monitor->name) >= MAX_RV_MONITOR_NAME_SIZE) {

s/>=/>/ no? The same check happened in patch 2. Thanks,

> +		pr_info("Monitor %s has a name longer than %d\n", monitor->name,
> +			MAX_RV_MONITOR_NAME_SIZE);