lkml.org 
[lkml]   [2009]   [Jun]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 5/5] tracing: reset iterator in t_start()
Li Zefan wrote:
>> Another version:
>> Since we have saved current (struct tracer *) in m->private in .next, in
>> .start, we don't need to call .next to find the one that should be
>> printed in 2nd or nth time.
>>
>
> I don't like this for 2 reasons.
>
> 1. It's strange that @pos is not incremented in next().
Yes, it's strang, but we know that @pos sometimes is not necessary, such in this
position.

>
> 2.
> t_stop()
> mutex_unlock()
> unregister_tracer(t)
> t_start()
> mutex_lock()
> t = m->private
> ...
> t = t-next.
>
> We access t->next though @t was unregistered. This is not
> good, though it does no harm here.
OK, it's a realy race problem if we call unregister_tracer.
btw: who realy calls this function? :)

Liming Wang
>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index cae34c6..02cdccc 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -2055,8 +2055,6 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
>> {
>> struct tracer *t = m->private;
>>
>> - (*pos)++;
>> -
>> if (t)
>> t = t->next;
>>
>> @@ -2068,11 +2066,8 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
>> static void *t_start(struct seq_file *m, loff_t *pos)
>> {
>> struct tracer *t = m->private;
>> - loff_t l = 0;
>>
>> mutex_lock(&trace_types_lock);
>> - for (; t && l < *pos; t = t_next(m, t, &l))
>> - ;
>>
>> return t;
>> }
>>
>>
>



\
 
 \ /
  Last update: 2009-06-23 09:39    [from the cache]
©2003-2011 Jasper Spaans