Re: rcu: BUG: spinlock recursion on CPU#3, trinity-child19/5970

Paul E. McKenney
2012-07-02T11:36:09Z

On Mon, Jul 02, 2012 at 12:32:19PM +0200, Peter Zijlstra wrote:
> On Fri, 2012-06-29 at 23:40 +0200, Sasha Levin wrote:
> >
> > The bad news are that what you saw was a lockdep enabled run
> > (CONFIG_PROVE_RCU is enabled, and lockdep was enabled). There were no
> > lockdep warnings at any point while reproducing it.
>
> rcu_switch_from() -> rcu_preempt_note_context_switch() is called _after_
> the lockdep context switch annotation. Therefore lockdep things the prev
> task isn't holding any locks anymore.

In other words, moving rcu_preempt_note_context_switch() deeper into
the scheduler is totally bogus, and I need to move it back out into the
original rcu_note_context_switch(), reverting 616c310e (Move PREEMPT_RCU
preemption to switch_to() invocation), correct?

Sigh. "It seemed like a good idea at the time."

Thanx, Paul