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Date: Mon, 23 Mar 2009 20:47:07 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Greg Kroah-Hartman <gregkh@suse.de>
Subject: Re: [PATCH 3/5] tracing/ftrace: check if debugfs is registered
	before creating files
Message-ID: <20090323194705.GE5988@nowhere>
References: <1237759847-21025-1-git-send-email-fweisbec@gmail.com> <1237759847-21025-3-git-send-email-fweisbec@gmail.com> <alpine.DEB.2.00.0903231517410.3578@gandalf.stny.rr.com>
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On Mon, Mar 23, 2009 at 03:18:49PM -0400, Steven Rostedt 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@suse.de>
> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.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
> 

Indeed, I lacked a bit of imagination here :-)

Thanks!