Re: 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault

Paul E. McKenney
2011-05-13T07:18:57Z

On Thu, May 12, 2011 at 12:05:24PM -0400, Valdis.Kletnieks@vt.edu wrote:
> On Thu, 12 May 2011 02:47:05 PDT, "Paul E. McKenney" said:
> > On Wed, May 11, 2011 at 07:11:34PM -0400, Valdis.Kletnieks@vt.edu wrote:
> > > My source has this:
> > >
> > > raw_spin_lock_irqsave(&rnp->lock, flags);
> > > rnp->wakemask |= rdp->grpmask;
> > > invoke_rcu_node_kthread(rnp);
> > > raw_spin_unlock_irqrestore(&rnp->lock, flags);
> > >
> > > the last 2 lines swapped from what you diffed against. I can easily work around
> > > that, except it's unclear what the implications of the invoke_rcu moving outside
> > > of the irq save/restore pair (or if it being inside is the actual root cause)...
> >
> > Odd...
> >
> > This looks to me like a recent -next -- I do not believe that straight
> > mmotm has rcu_cpu_kthread_timer() in it. The patch should apply to the
> > last few days' -next kernels.
>
> Ah. Found it. Your tree and current linux-next include this commit:
>
> commit 1217ed1ba5c67393293dfb0f03c353b118dadeb4
> tree a765356c8418e134de85fd05d9fe6eda41de859c tree | snapshot
> parent 29ce831000081dd757d3116bf774aafffc4b6b20 commit | diff
> rcu: permit rcu_read_unlock() to be called while holding runqueue locks
>
> which includes this chunk:
>
> @@ -1546,8 +1531,8 @@ static void rcu_cpu_kthread_timer(unsigned long arg)
>
> raw_spin_lock_irqsave(&rnp->lock, flags);
> rnp->wakemask |= rdp->grpmask;
> - invoke_rcu_node_kthread(rnp);
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
> + invoke_rcu_node_kthread(rnp);
> }
>
>
> but that was committed 4 days ago, and Andrew pulled linux-next for the -mmotm
> 6 days ago, so it's not in there. The *rest* of your recent commits appear to
> be in there though. So that explains the patch failure to apply.

Whew!!! ;-)

Thanx, Paul