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

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Message-ID: <495E68F5.5010309@gmail.com>
Date:	Fri, 02 Jan 2009 20:20:21 +0100
From:	Roel Kluin <roel.kluin@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] ftrace: unsigned idx cannot be less than 0

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.

If we turn idx in a signed int, isn't it true that
in kernel/trace/ftrace.c, line 806:

retry:
if (iter->idx >= iter->pg->index) {
	...
} else {
	iter->idx++;
	if ( a certain rec-> and iter->flags )
		goto retry;
}

since iter->pg->index is an unsigned long, when larger than INT_MAX this
could result in an endless loop?

Roel
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