Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probeevent files are open

[Steven Rostedt]

On Thu, 2013-08-01 at 16:33 +0200, Oleg Nesterov wrote:
> On 08/01, Steven Rostedt wrote:
> >
> > On Thu, 2013-08-01 at 15:34 +0200, Oleg Nesterov wrote:
> > > >
> > > >   __unregister_trace_probe(tp);
> > > >   list_del(&tp->list)
> > > >   unregister_probe_event(tp) <-- fails!
> > > >   free_trace_probe(tp)
> > >
> > > Yes. But again, this doesn't explain why unregister_probe_event()->
> > > __trace_remove_event_call() can't simply proceed and
> > > do ftrace_event_enable_disable() + remove_event_from_tracers().
> >
> > The problem is with the soft disable.
> 
> Exactly! This is another (also unlikely) race we need to prevent.
> 

Is there a race even with these patches? I don't see one. To link a
function to an event (set the soft disable mode), the event_mutex is
taken. If the event is gone, it wont be able to link. If the soft
disable is attached (after found and set under event_mutex), the event
can't be deleted.

Or are you just saying that these patches fix that case too?

-- Steve


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