linux-kernel - Re: oops in tracepoint_update_probe_range() (was: Re: [oops -tip] : x86 AMD 64)

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Date:	Wed, 18 Mar 2009 18:27:50 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: oops in tracepoint_update_probe_range() (was: Re: [oops -tip]
	: x86 AMD 64)


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Wed, Mar 18, 2009 at 10:18:56PM +0530, Jaswinder Singh Rajput wrote:
> > On Wed, 2009-03-18 at 17:35 +0100, Ingo Molnar wrote:
> > > * Jaswinder Singh Rajput <jaswinder@...nel.org> wrote:
> > > 
> > > > Good: f4c3c4cdb1de232
> > > > Bad : 1e08816af0bc345
> > > > 
> > > > Config:
> > > > http://userweb.kernel.org/~jaswinder/oops_20090318/config-hpdv5-tip-bad-20090318
> > > > 
> > > > oops:
> > > > http://userweb.kernel.org/~jaswinder/oops_20090318/oops_page1.jpg
> > > > http://userweb.kernel.org/~jaswinder/oops_20090318/oops_page2.jpg
> > > > http://userweb.kernel.org/~jaswinder/oops_20090318/oops_page3.jpg
> > > > http://userweb.kernel.org/~jaswinder/oops_20090318/oops_page4.jpg
> > > > 
> > > > <freeze>
> > > 
> > > Steve, Frederic - the crashes above are in:
> > > 
> > > 	tracepoint_update_probe_range()
> > > 
> > > in a modular kernel apparently.
> > > 
> > 
> > This fixed the oops for me, Is this looks OK to you:
> > 
> > Subject: [PATCH] x86: tracepoint.c fix oops
> > 
> > BUG: unable to handle kernel NULL pointer dereference at (null)
> > IP: [<ffffffff8107d4de>] tracepoint_update_probe_range+0x1f/0x9b
> > PGD 13d5fb067 PUD 13d688067 PMD 0
> > Oops: 0000 [#1] SMP
> > 
> > Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@...il.com>
> > ---
> >  kernel/tracepoint.c |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> > index 7960274..80d1353 100644
> > --- a/kernel/tracepoint.c
> > +++ b/kernel/tracepoint.c
> > @@ -280,6 +280,8 @@ void tracepoint_update_probe_range(struct tracepoint *begin,
> >  
> >  	mutex_lock(&tracepoints_mutex);
> >  	for (iter = begin; iter < end; iter++) {
> > +		if (!iter)
> > +			goto out;
> >  		mark_entry = get_tracepoint(iter->name);
> >  		if (mark_entry) {
> >  			set_tracepoint(&mark_entry, iter,
> > @@ -288,6 +290,7 @@ void tracepoint_update_probe_range(struct tracepoint *begin,
> >  			disable_tracepoint(iter);
> >  		}
> >  	}
> > +out:
> >  	mutex_unlock(&tracepoints_mutex);
> >  }
> 
> 
> Ok, it should fix the crash.
> But I think the real problem remains: iter is not supposed to point to NULL,
> this is a section range:
> 
> tracepoint_update_probe_range(__start___tracepoints,
> 		__stop___tracepoints);
> 
> It seems to mean that the section is empty.

OK - so checking for !iter on entry and emitting a WARN_ONCE in that 
case ought to change the crash for a warning, right?

	Ingo
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