linux-kernel - Re: [PATCH 1/2] tracing/ftrace: handle more than one stat file per tracer

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Date:	Tue, 6 Jan 2009 12:28:32 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Subject: Re: [PATCH 1/2] tracing/ftrace: handle more than one stat file per
 tracer



On Tue, 6 Jan 2009, Frederic Weisbecker wrote:
> > > +
> > > +	if (all_stat_sessions) {
> > > +		for (i = 0; i < nb_sessions; i++) {
> > > +			session = all_stat_sessions[i];
> > > +			reset_stat_session(session);
> > > +			mutex_destroy(&session->stat_mutex);
> > > +			kfree(session);
> > > +		}
> > > +	}
> > > +	all_stat_sessions = kmalloc(sizeof(struct tracer_stat_session *) * nb,
> > > +				    GFP_KERNEL);
> > 
> > You want this to be kzalloc.
> > 
> > > +	if (!all_stat_sessions)
> > > +		return -ENOMEM;
> > > +
> > > +	for (i = 0; i < nb; i++) {
> > > +		session = kmalloc(sizeof(struct tracer_stat_session) * nb,
> > > +				  GFP_KERNEL);
> > 
> > Not so important, but you probably want to do it here too.
> > 
> > > +		if (!session)
> > > +			goto free_sessions;
> > > +
> > > +		INIT_LIST_HEAD(&session->stat_list.list);
> > > +		mutex_init(&session->stat_mutex);
> > > +		session->ts = &ts[i];
> > > +		all_stat_sessions[i] = session;
> > > +	}
> > > +	nb_sessions = nb;
> > > +	return 0;
> > > +
> > > +free_sessions:
> > > +
> > > +	for (j = 0; j < i; j++)
> > > +		kfree(all_stat_sessions[i]);
> > 
> > With out the kzalloc above, this may crash the kernel, because
> > all_stat_sessions[i] might not be NULL when they were not initialized.
> 
> 
> I'm not sure. j will not go through indexes of rooms that weren't allocated.

Ah, OK, my eyes confused i's and j's so I did not notice the loop to last 
failed. Which is strange because I write similar code :-/.

-- Steve
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