Re: [PATCH 5/5] tracing: reset iterator in t_start()

From: Wang Liming
Date: Tue Jun 23 2009 - 03:35:33 EST

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()
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;

- for (; t && l < *pos; t = t_next(m, t, &l))
- ;

return t;

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