linux-kernel - Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open

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Date:	Thu, 1 Aug 2013 16:46:22 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe
	event files are open

On 08/01, Steven Rostedt wrote:
>
> 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?

Sorry for confusion,

> I don't see one.

Neither me, but only with these changes.

I meant that this is another reason why trace_remove_event_call() should
fail and the caller should obviously abort in this case.

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

Yes, sorry.

Oleg.

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