linux-kernel - Re: [PATCH 1/1] tracing: Simplify trace_array

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Message-ID: <1374255311.3356.15.camel@gandalf.local.home>
Date:	Fri, 19 Jul 2013 13:35:11 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] tracing: Simplify trace_array_get()

On Fri, 2013-07-19 at 19:20 +0200, Oleg Nesterov wrote:

> Yes. But unless I missed something again this logic doesn't look exactly
> correct. Because it seems that trace_array_get() can succeed when it
> shoudn't.
> 
> trace_array_get() can race with instance_delete() + new_instance_create(),
> and _create()->kzalloc() can return the same memory which was freed by
> _delete().
> 
> No?

Correct, but I don't see that as a major problem, do you?

What would happen in that case, is that an event might be enabled or
disabled in another buffer instance. As that can only happen by the root
user, it would be the root user doing multiple things at the same time
to cause it. They might get a strange result at worse, but that would
also mean they were trying to add and delete instances while reading
those same instances. Bad root, bad!

-- Steve


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