On Wed, 19 Jun 2019 01:14:09 +0900
Masami Hiramatsu <mhira...@kernel.org> wrote:
> On Mon, 17 Jun 2019 21:56:43 -0400
> Steven Rostedt <rost...@goodmis.org> wrote:
>
> > > +static nokprobe_inline struct trace_kprobe *
> > > +trace_kprobe_primary_from_call(struct trace_event_call *call)
> > > +{
> > > + struct trace_probe *tp = trace_probe_primary_from_call(call);
> > > +
> > > + return container_of(tp, struct trace_kprobe, tp);
> >
> >
> > Hmm, is there a possibility that trace_probe_primary_from_call() may
> > not have a primary?
>
> Good question! Of course if given event_call is not a kprobe event,
> it doesn't have primary (or any) trace_probe. But that must not happen
> unless user misuses it.
> And that list never be the empty, when the last trace probe is released,
> the event_call also unregistered and released. See unregister_trace_kprobe()
> for details. If there is no siblings on the list, the event_call is also
> unregistered before unregistering kprobes, and after unregistering kprobes
> the list is unlinked.
> (Note that unregister_kprobe() will wait a quiescence period
> before return. This means all probe handlers are done before that.)
Yeah, I thought something like that. But perhaps the
trace_probe_primary_from_call() code should add a WARN_ON() is the list
is empty.
>
> > >
> > > - ret = __enable_trace_kprobe(tk);
> > > - if (ret) {
> > > + enabled = false;
> > > + list_for_each_entry(pos, trace_probe_probe_list(tp), list) {
> > > + tk = container_of(pos, struct trace_kprobe, tp);
> > > + ecode = __enable_trace_kprobe(tk);
> > > + if (ecode)
> > > + ret = ecode; /* Save the last error code */
> > > + else
> > > + enabled = true;
> >
> > So, if we have some enabled but return an error code, what should a
> > caller think of that? Wouldn't it be an inconsistent state?
>
> Oops, good catch!
> This part is related to caller (ftrace/perf) so should be more careful.
> Usually, kprobe enablement should not fail. If one of them has
> gone (like a probe on unloaded module), it can be fail but that
> should be ignored. I would like to add some additional check so that
> - If all kprobes are on the module which is unloaded, enablement
> must be failed and return error.
> - If any kprobe is enabled, and others are on non-exist modules,
> it should succeeded and return OK.
> - If any kprobe caused an error not because of unloaded module,
> all other enablement should be canceled and return error.
>
> Is that OK for you?
>
Sounds good to me.
-- Steve
