linux-kernel - Re: [PATCH v3 12/33] tracing: Add variable support to hist triggers

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Date:   Thu, 12 Oct 2017 08:23:47 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel.opensrc@...il.com, joelaf@...gle.com,
        mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
        rajvi.jingar@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH v3 12/33] tracing: Add variable support to hist triggers

Hi Tom,

On Wed, Oct 11, 2017 at 08:33:17AM -0500, Tom Zanussi wrote:
> On Mon, 2017-10-09 at 12:27 +0900, Namhyung Kim wrote:
> > On Fri, Sep 22, 2017 at 02:59:52PM -0500, Tom Zanussi wrote:
> > > Variables set as above can be used by being referenced from another
> > > event, as described in a subsequent patch.
> > 
> > That means, a variable should be unique (in a tracing instance at least).
> > 
> 
> Not exactly - I thought it would be too restrictive to force users to
> come up with names that would be unique across an instance, so made them
> unique to events.  So users can use the same variable name for triggers
> on multiple events, and in cases where there are multiple events with
> the same name, use the fully-qualified subsys.event_name.variable_name
> name to disambiguate them.  If there is only one event with the given
> name, thus no ambiguity, specifying the bare variable name suffices.
> Again the intent is to make the common case as simple as possible, but
> allow for more complex cases without requiring naming gymnastics from
> the user.

Agreed.  Thanks for the explanation.


[SNIP]

> > > +static int parse_var_defs(struct hist_trigger_data *hist_data)
> > > +{
> > > +	char *s, *str, *var_name, *field_str;
> > > +	unsigned int i, j, n_vars = 0;
> > > +	int ret = 0;
> > > +
> > > +	for (i = 0; i < hist_data->attrs->n_assignments; i++) {
> > > +		str = hist_data->attrs->assignment_str[i];
> > > +		for (j = 0; j < TRACING_MAP_VARS_MAX; j++) {
> > > +			field_str = strsep(&str, ",");
> > > +			if (!field_str)
> > > +				break;
> > > +
> > > +			var_name = strsep(&field_str, "=");
> > > +			if (!var_name || !field_str) {
> > > +				ret = -EINVAL;
> > > +				goto free;
> > > +			}
> > > +
> > > +			s = kstrdup(var_name, GFP_KERNEL);
> > > +			if (!s) {
> > > +				ret = -ENOMEM;
> > > +				goto free;
> > > +			}
> > > +			hist_data->attrs->var_defs.name[n_vars] = s;
> > > +
> > > +			s = kstrdup(field_str, GFP_KERNEL);
> > > +			if (!s) {
> > > +				ret = -ENOMEM;
> > > +				goto free;
> > 
> > It seems that it might leak the copy of var_name here..
> > 
> 
> Unless I'm missing something, the free_var_defs() should handle this
> case too...

But the var_defs.n_vars was not increased at this point.

Thanks,
Namhyung


> > 
> > > +			}
> > > +			hist_data->attrs->var_defs.expr[n_vars++] = s;
> > > +
> > > +			hist_data->attrs->var_defs.n_vars = n_vars;
> > > +
> > > +			if (n_vars == TRACING_MAP_VARS_MAX)
> > > +				goto free;
> > > +		}
> > > +	}
> > > +
> > > +	return ret;
> > > + free:
> > > +	free_var_defs(hist_data);
> > > +
> > > +	return ret;
> > > +}
> > > +
> 
>