Re: [PATCH RFC tip/core/rcu 14/18] rcu: lockdep check for exitingto user space as RCU reader

From: Paul E. McKenney
Date: Wed Dec 16 2009 - 10:11:29 EST

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@xxxxxxxxxxxxxxxxxx>
> >
> > 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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