linux-kernel - Re: [PATCH] ftrace: unsigned idx cannot be less than 0

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Message-ID: <alpine.DEB.1.10.0901061048260.10871@gandalf.stny.rr.com>
Date:	Tue, 6 Jan 2009 10:49:49 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Roel Kluin <roel.kluin@...il.com>,
	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Liming Wang <liming.wang@...driver.com>
Subject: Re: [PATCH] ftrace: unsigned idx cannot be less than 0


[ added Liming to CC ]

On Fri, 2 Jan 2009, Frederic Weisbecker wrote:

> On Fri, Jan 02, 2009 at 03:49:43PM +0100, Roel Kluin wrote:
> > // vi kernel/trace/ftrace.c +787
> > struct ftrace_iterator {
> > ...
> >         unsigned                idx;
> > ...
> > };
> > 
> > idx is unsigned and cannot be less than 0.
> > 
> > Signed-off-by: Roel Kluin <roel.kluin@...il.com>
> > ---
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 2f32969..a344add 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -842,7 +842,7 @@ static void *t_start(struct seq_file *m, loff_t *pos)
> >  	void *p = NULL;
> >  
> >  	if (*pos > 0) {
> > -		if (iter->idx < 0)
> > +		if (iter->idx == 0)
> >  			return p;
> >  		(*pos)--;
> >  		iter->idx--;
> 
> 
> Hi Roel,
> 
> I'm not sure this is the right fix.
> If you look at t_next, if there is no more page to look at,
> iter_idx takes -1.
> 
> A 0 value would mean: we are in the first index on the page, which means
> there is something to read and we don't want to return NULL.
> 
> I guess that would be better to turn idx into a signed int.

Correct. This bug was added by:

  50cdaf08a8ec1d7f43987705da7aff7cf949708f
  ftrace: improve seq_operation of ftrace

So the correct fix is to turn it into a signed int.

Thanks,

-- Steve
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