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

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Date:	Fri, 18 Oct 2013 08:34:48 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Geyslan Gregório Bem <geyslan@...il.com>
Cc:	kernel-br <kernel-br@...glegroups.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	open list <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [PATCH] tracing: fix referencing after memory freeing and
 refactors code

On Fri, 18 Oct 2013 08:02:32 -0300
Geyslan Gregório Bem <geyslan@...il.com> wrote:

> >>
> >> 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 as it just
> >> reassigns it anyway.
> >>
> >> We could add a tracing_is_disabled() function to test instead.
> >
> > Nice, I can do it.
> >
> > Questions:
> 
> I realized that here not:

Right, tracing_is_disabled() should not be called as a fops method.

> >
> > 1267 static const struct file_operations ftrace_enable_fops = {
> > 1268         .open = tracing_open_generic,
> > ...
> > 1286 static const struct file_operations ftrace_event_filter_fops = {
> > 1287         .open = tracing_open_generic,
> > ...
> > 1317 static const struct file_operations ftrace_show_header_fops = {
> > 1318         .open = tracing_open_generic,
> 
> Tell me about this other case:
> >
> > Are that structures in same case? Their 'open' can be replaced to the
> > new 'tracing_is_disabled()?
> >
> > I think that 'subsystem_open()' can be also refactored to use the
> > about to rise 'tracing_is_disabled()'. Am I right?
> > 1096         ret = tracing_open_generic(inode, filp);

Hmm, no, it needs the assignment too. But perhaps we could just open
code it. The tracing_open_generic() is more for fops then to be a
helper for functions that don't use it for their .open routine.

Thus, for subsystem_open() you could have at the start:

	if (tracing_is_disabled())
		return -ENODEV;


Then have:

-       ret = tracing_open_generic(inode, filp);
-       if (ret < 0) {
-               trace_array_put(tr);
-               put_system(dir);
-       }
+       filp->private_data = dir;


-- Steve


> 
> Regards,
> -- Geyslan

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