linux-kernel - Re: [PATCH] tracing: fix referencing after memory freeing and refactors code

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Date:	Sat, 19 Oct 2013 14:43:12 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Geyslan G. Bem" <geyslan@...il.com>, kernel-br@...glegroups.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	open list <linux-kernel@...r.kernel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [PATCH] tracing: fix referencing after memory freeing and
	refactors code

On 10/17, Steven Rostedt wrote:
>
> On Thu, 17 Oct 2013 22:44:56 -0300
> "Geyslan G. Bem" <geyslan@...il.com> wrote:
>
> > and fix the possible 'dir'
> > assignment after freeing it.

This should be safe afaics, nobody will use it anyway. Even
subsystem_release() won't be called if .open() fails. But I agree
this doesn't look good.

> I'm thinking of just nuking the tracing_open_generic() here. The only
> thing it does here is the tracing_disabled check. The assignment of
> inode->i_private to filp->private_data is pointless

The same for ftrace_enable_fops() and ftrace_event_filter_fops() at
least. The users of event_file_data() do not use ->private_data.

OTOH, say, trace_format_open() doesn't check tracing_disabled, so

> We could add a tracing_is_disabled() function to test instead.

perhaps it can have more callers.

Oleg.

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