Date:	Thu, 29 Oct 2015 13:37:50 -0500
From:	Tom Zanussi <tom.zanussi@...ux.intel.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	rostedt@...dmis.org, daniel.wagner@...-carit.de,
	masami.hiramatsu.pt@...achi.com, josh@...htriplett.org,
	andi@...stfloor.org, mathieu.desnoyers@...icios.com,
	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 09/28] tracing: Add 'hist' event trigger command

On Thu, 2015-10-29 at 18:11 +0900, Namhyung Kim wrote:
> On Thu, Oct 22, 2015 at 01:14:13PM -0500, Tom Zanussi wrote:
> > 'hist' triggers allow users to continually aggregate trace events,
> > which can then be viewed afterwards by simply reading a 'hist' file
> > containing the aggregation in a human-readable format.
> > 
> > The basic idea is very simple and boils down to a mechanism whereby
> > trace events, rather than being exhaustively dumped in raw form and
> > viewed directly, are automatically 'compressed' into meaningful tables
> > completely defined by the user.
> > 
> > This is done strictly via single-line command-line commands and
> > without the aid of any kind of programming language or interpreter.
> > 
> > A surprising number of typical use cases can be accomplished by users
> > via this simple mechanism.  In fact, a large number of the tasks that
> > users typically do using the more complicated script-based tracing
> > tools, at least during the initial stages of an investigation, can be
> > accomplished by simply specifying a set of keys and values to be used
> > in the creation of a hash table.
> > 
> > The Linux kernel trace event subsystem happens to provide an extensive
> > list of keys and values ready-made for such a purpose in the form of
> > the event format files associated with each trace event.  By simply
> > consulting the format file for field names of interest and by plugging
> > them into the hist trigger command, users can create an endless number
> > of useful aggregations to help with investigating various properties
> > of the system.  See Documentation/trace/events.txt for examples.
> > 
> > hist triggers are implemented on top of the existing event trigger
> > infrastructure, and as such are consistent with the existing triggers
> > from a user's perspective as well.
> > 
> > The basic syntax follows the existing trigger syntax.  Users start an
> > aggregation by writing a 'hist' trigger to the event of interest's
> > trigger file:
> > 
> >   # echo hist:keys=xxx [ if filter] > event/trigger
> > 
> > Once a hist trigger has been set up, by default it continually
> > aggregates every matching event into a hash table using the event key
> > and a value field named 'hitcount'.
> > 
> > To view the aggregation at any point in time, simply read the 'hist'
> > file in the same directory as the 'trigger' file:
> > 
> >   # cat event/hist
> > 
> > The detailed syntax provides additional options for user control, and
> > is described exhaustively in Documentation/trace/events.txt and in the
> > virtual tracing/README file in the tracing subsystem.
> > 
> > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> > ---
> 
> [SNIP]
> > +static int event_hist_trigger_func(struct event_command *cmd_ops,
> > +				   struct trace_event_file *file,
> > +				   char *glob, char *cmd, char *param)
> > +{
> > +	unsigned int hist_trigger_bits = TRACING_MAP_BITS_DEFAULT;
> > +	struct event_trigger_data *trigger_data;
> > +	struct hist_trigger_attrs *attrs;
> > +	struct event_trigger_ops *trigger_ops;
> > +	struct hist_trigger_data *hist_data;
> > +	char *trigger;
> > +	int ret = 0;
> > +
> > +	if (!param)
> > +		return -EINVAL;
> > +
> > +	/* separate the trigger from the filter (k:v [if filter]) */
> > +	trigger = strsep(&param, " \t");
> > +	if (!trigger)
> > +		return -EINVAL;
> > +
> > +	attrs = parse_hist_trigger_attrs(trigger);
> > +	if (IS_ERR(attrs))
> > +		return PTR_ERR(attrs);
> > +
> > +	if (!attrs->keys_str)
> > +		return -EINVAL;
> 
> Wouldn't it leak the attrs?
> 
> 
> > +
> > +	if (attrs->map_bits)
> > +		hist_trigger_bits = attrs->map_bits;
> > +
> > +	hist_data = create_hist_data(hist_trigger_bits, attrs, file);
> > +	if (IS_ERR(hist_data))
> > +		return PTR_ERR(hist_data);
> 
> It also can leak the attrs IMHO.
> 
> 
> > +
> > +	trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
> > +
> > +	ret = -ENOMEM;
> > +	trigger_data = kzalloc(sizeof(*trigger_data), GFP_KERNEL);
> > +	if (!trigger_data)
> > +		goto out;
> 
> Here, the hist_data and the attr can be leaked.
> 

You're correct, thanks for catching all of the above, will fix in the
next version..

Thanks,

Tom

> Thanks,
> Namhyung
> 
> 
> > +
> > +	trigger_data->count = -1;
> > +	trigger_data->ops = trigger_ops;
> > +	trigger_data->cmd_ops = cmd_ops;
> > +
> > +	INIT_LIST_HEAD(&trigger_data->list);
> > +	RCU_INIT_POINTER(trigger_data->filter, NULL);
> > +
> > +	trigger_data->private_data = hist_data;
> > +
> > +	if (glob[0] == '!') {
> > +		cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
> > +		ret = 0;
> > +		goto out_free;
> > +	}
> > +
> > +	if (!param) /* if param is non-empty, it's supposed to be a filter */
> > +		goto out_reg;
> > +
> > +	if (!cmd_ops->set_filter)
> > +		goto out_reg;
> > +
> > +	ret = cmd_ops->set_filter(param, trigger_data, file);
> > +	if (ret < 0)
> > +		goto out_free;
> > + out_reg:
> > +	ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
> > +	/*
> > +	 * The above returns on success the # of triggers registered,
> > +	 * but if it didn't register any it returns zero.  Consider no
> > +	 * triggers registered a failure too.
> > +	 */
> > +	if (!ret) {
> > +		ret = -ENOENT;
> > +		goto out_free;
> > +	} else if (ret < 0)
> > +		goto out_free;
> > +	/* Just return zero, not the number of registered triggers */
> > +	ret = 0;
> > + out:
> > +	return ret;
> > + out_free:
> > +	if (cmd_ops->set_filter)
> > +		cmd_ops->set_filter(NULL, trigger_data, NULL);
> > +
> > +	kfree(trigger_data);
> > +
> > +	destroy_hist_data(hist_data);
> > +	goto out;
> > +}


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