Re: [tip:tracing/ftrace] tracing: fix oops in tracepoint_update_probe_range()

[Ingo Molnar <mingo@elte.hu>]

* Jaswinder Singh Rajput <jaswinder@kernel.org> wrote:

> On Wed, 2009-03-18 at 17:51 +0000, Jaswinder Singh Rajput wrote:
> > Commit-ID:  966a6fdf6210e3ac8ce00b61cd1107cdf97ce744
> > Gitweb:     http://git.kernel.org/tip/966a6fdf6210e3ac8ce00b61cd1107cdf97ce744
> > Author:     Jaswinder Singh Rajput <jaswinder@kernel.org>
> > AuthorDate: Wed, 18 Mar 2009 22:18:56 +0530
> > Commit:     Ingo Molnar <mingo@elte.hu>
> > CommitDate: Wed, 18 Mar 2009 18:48:43 +0100
> > 
> > tracing: fix oops in tracepoint_update_probe_range()
> > 
> > Change this crash:
> > 
> >  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
> > 
> > To a more debuggable WARN_ONCE().
> > 
> > Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
> > Cc: Frederic Weisbecker <fweisbec@gmail.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > LKML-Reference: <1237394936.3132.1.camel@localhost.localdomain>
> > [ moved the check outside the lock and added a WARN_ON(). ]
> > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > 
> > 
> > ---
> >  kernel/tracepoint.c |    9 +++++++--
> >  1 files changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> > index 7960274..dd15df9 100644
> > --- a/kernel/tracepoint.c
> > +++ b/kernel/tracepoint.c
> > @@ -272,12 +272,17 @@ static void disable_tracepoint(struct tracepoint *elem)
> >   *
> >   * Updates the probe callback corresponding to a range of tracepoints.
> >   */
> > -void tracepoint_update_probe_range(struct tracepoint *begin,
> > -	struct tracepoint *end)
> > +void
> > +tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
> >  {
> >  	struct tracepoint *iter;
> >  	struct tracepoint_entry *mark_entry;
> >  
> > +	if (!iter) {
> > +		WARN_ON_ONCE(1);
> > +		return;
> > +	}
> > +
> >  	mutex_lock(&tracepoints_mutex);
> >  	for (iter = begin; iter < end; iter++) {
> >  		mark_entry = get_tracepoint(iter->name);
> 
> my original patch was correct.

It might have worked but it was rather ugly: it took the 
tracepoints_mutex for no reason.

The clean fix to skip zero-sized sections early in the function, 
without taking any lock, and without emitting a warning.

	Ingo