linux-kernel - Re: [QUESTION] trace_function_graph: consumed event may be invalid

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Date:	Tue, 30 Jun 2009 12:54:18 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [QUESTION] trace_function_graph: consumed event may be invalid

On Tue, Jun 30, 2009 at 04:14:36PM +0800, Lai Jiangshan wrote:
> 
> In get_return_for_leaf() {
> 	......
> 	ring_buffer_consume()
> 	......
> 	access to @curr->ent.pid
> }
> 
> @curr is saved at consumed event, if this event is the last event
> in the page, the ring_buffer may reuse the page. It will become invalid.


Indeed!

 
> Is there any other code to ensure it valid when we `cat trace_pipe`?
> 
> Lai.


The only solution I see is to do a copy of the entry before consuming it.
I'll try that, thanks for your report!

Frederic.

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