linux-kernel - Re: [PATCH 3/5] tracing/ftrace: check if debugfs is registered before creating files

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Message-ID: <alpine.DEB.2.00.0903231517410.3578@gandalf.stny.rr.com>
Date:	Mon, 23 Mar 2009 15:18:49 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH 3/5] tracing/ftrace: check if debugfs is registered before
 creating files


On Sun, 22 Mar 2009, Frederic Weisbecker wrote:

> Impact: fix a crash with ftrace={nop,boot} parameter
> 
> If the nop or initcall tracers are launched as boot tracers,
> they will attempt to create their option directory and files.
> But these tracers are registered very early and then assigned
> as "boot tracers" very early if asked to.
> 
> Since they do this before debugfs has been registered (core initcall),
> a crash is triggered.
> 
> Another early tracers could also come later. So we fix it by
> checking if debugfs is initialized before creating the root
> tracing directory.
> 
> Cc: Greg Kroah-Hartman <gregkh@...e.de>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  kernel/trace/trace.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ace685c..f0e1337 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3513,6 +3513,9 @@ struct dentry *tracing_init_dentry(void)
>  	if (d_tracer)
>  		return d_tracer;
>  
> +	if (!debugfs_initialized())
> +		return NULL;
> +
>  	d_tracer = debugfs_create_dir("tracing", NULL);
>  

Hmm, those tracers should separate out the debugfs code, and put it into 
a fs_initcall(), where debugfs should already initialized.

-- Steve

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