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

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Message-ID: <20090323192212.GA23842@elte.hu>
Date:	Mon, 23 Mar 2009 20:22:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	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


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> 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.

indeed, this seems much cleaner and we'll have the debugfs 
structures initialized as well.

	Ingo
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