On Tue, Mar 28, 2017 at 10:28:55PM -0400, Steven Rostedt wrote:
> On Wed, 29 Mar 2017 11:20:37 +0900
> Namhyung Kim <[email protected]> wrote:
>
>
> > > Actually, if this is called after event_trace_del_tracer(), the tr is
> > > already invisible and nothing new should change.
> >
> > I don't follow. After event_trace_del_tracer(), the tr is invisible
> > from the probe of event tracing but still is visible from the probe of
> > function tracing, right?
>
> Well, nothing should be able to get to the set_ftrace_filter file when
> there. Because of the tr->ref count. But keeping the lock is safer
> regardless, and it's not a fast path, so the extra overhead if the lock
> isn't needed is no big deal.
Oh, I meant if a pid filter was already set when removing the
instance. Function filters should be inactive since function tracer
was finished (via tracing_set_nop), but the probe on sched_switch
event (for pid filter) is still active and references the tr.
Thanks,
Namhyung
>
> >
> > >
> > > Make a wrapper around clear_ftrace_pids() and call that instead. We
> > > don't even need to take a lock, but as I see there's a lockdep test for
> > > ftrace_lock, we should still do so just to be safe.
> >
> > Right, that's why I call ftrace_pid_reset() instead of
> > clear_ftrace_pids(). So do you prefer adding a new wrapper like below
> > rather than reusing ftrace_pid_reset() with a new argument?
>
> Yes, because the bool passed in is confusing. A separate function like
> below is more descriptive.
>
> -- Steve
>
> >
> > Thanks,
> > Namhyung
> >
> >
> > >
> > > void ftrace_clear_pids(struct trace_array *tr)
> > > {
> > > mutex_lock(&ftrace_lock);
> > >
> > > clear_ftrace_pids(tr);
> > >
> > > mutex_unlock(&ftrace_lock);
> > > }
