linux-kernel - Re: [GIT PULL] RCU changes for v3.3

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Message-ID: <20120124170414.GA20878@somewhere>
Date:	Tue, 24 Jan 2012 18:04:17 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] RCU changes for v3.3

On Tue, Jan 24, 2012 at 08:53:13AM -0800, Paul E. McKenney wrote:
> On Tue, Jan 24, 2012 at 05:25:12PM +0100, Eric Dumazet wrote:
> > Le jeudi 05 janvier 2012 à 14:54 +0100, Ingo Molnar a écrit :
> > > Linus,
> > > 
> > > Please pull the latest core-rcu-for-linus git tree from:
> > > 
> > >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-rcu-for-linus
> > > 
> > >  Thanks,
> > 
> > Hi guys
> > 
> > New lockdep warning here :
> 
> Hmmm...  Looks like tracing from within the inner idle loop.
> 
> Because RCU ignores CPUs in the inner idle loop (after the call to
> rcu_idle_enter()), RCU read-side critical sections are not legal there.
> 
> One approach would be to delay the call to rcu_idle_enter() until after
> the tracing is done, and to ensure that the call to rcu_idle_exit() happens
> before any tracing.  I am not seeing perf_trace_power(), so need to
> update and look again.  Or are you looking at -next rather than mainline?

perf_trace_power() is automatically generated by include/trace/ftrace.h
This is a tracepoint handler so we don't need to worry about it. The problem
is the call to the tracepoint itself.
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