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    SubjectRe: [PATCH 5/5] tracing: reset iterator in t_start()
    > 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().

    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.

    > 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;
    > }
    >
    >


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