Date: Fri, 28 Feb 2014 17:05:53 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Vince Weaver <vincent.weaver@maine.edu>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot
Message-ID: <20140228170553.49f77108@gandalf.local.home>
In-Reply-To: <20140228215511.GB6835@laptop.programming.kicks-ass.net>
References: <530FC1C6.5040209@zytor.com>
	<20140227183008.6be081b7@gandalf.local.home>
	<530FCE6C.4080808@zytor.com>
	<alpine.DEB.2.10.1402271957380.6210@vincent-weaver-1.um.maine.edu>
	<20140228203405.GH11910@linux.vnet.ibm.com>
	<20140228154716.0198d7cb@gandalf.local.home>
	<20140228205409.GB14089@laptop.programming.kicks-ass.net>
	<20140228211733.GK11910@linux.vnet.ibm.com>
	<20140228212700.GH14089@laptop.programming.kicks-ass.net>
	<20140228215150.GM11910@linux.vnet.ibm.com>
	<20140228215511.GB6835@laptop.programming.kicks-ass.net>
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On Fri, 28 Feb 2014 22:55:11 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, Feb 28, 2014 at 01:51:50PM -0800, Paul E. McKenney wrote:
> > On Fri, Feb 28, 2014 at 10:27:00PM +0100, Peter Zijlstra wrote:
> > > On Fri, Feb 28, 2014 at 01:17:33PM -0800, Paul E. McKenney wrote:
> > > > This code isn't running in idle context is it?  If so, RCU will happily
> > > > free out from under it.  CONFIG_PROVE_RCU should detect this sort of thing,
> > > > though.
> > > 
> > > Well, interrupts/NMIs can happen when idle, but the interrupt/NMI
> > > entry code deals with the idle state AFAIK.
> > 
> > Yep, rcu_irq_enter() and rcu_nmi_enter() deal with that.  More worried
> > about this being code invoked from some energy-efficiency driver or
> > another within the idle loop.
> 
> Right, so any tracepoint can end up there; but I thought there was
> already the rule that tracepoints needed RCU enabled.

There is and we have special tracepoint caller for those cases we want a
tracepoint out of RCU scope. These will reactivate rcu in the
tracepoint code.

  trace_<tp_name>_rcuidle(...)

-- Steve
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