linux-kernel - Re: [PATCH RFC tip/core/rcu 14/18] rcu: lockdep check for exiting to user space as RCU reader

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Message-ID: <20091216151111.GA6744@linux.vnet.ibm.com>
Date:	Wed, 16 Dec 2009 07:11:11 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com
Subject: Re: [PATCH RFC tip/core/rcu 14/18] rcu: lockdep check for exiting
	to user space as RCU reader

On Wed, Dec 16, 2009 at 11:24:42AM +0100, Peter Zijlstra wrote:
> On Tue, 2009-12-15 at 15:02 -0800, Paul E. McKenney wrote:
> > From: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > Proposed for 2.6.34, not for inclusion.
> > 
> > It is illegal to return to user-space execution while running within an
> > RCU read-side critical section.  It turns out that CONFIG_TREE_PREEMPT_RCU
> > has enough information lying around to detect this, so add the checks
> > to lockdep (CONFIG_PROVE_LOCKING).
> 
> But uhm, we already track the rcu read lock as a regular lockdep lock,
> so it should already check this, no?

I guess I can drop that patch, then.  ;-)

Thank you for looking this over!

							Thanx, Paul
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