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    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;
    >> }
    >>
    >>
    >



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