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

Valdis.Kletnieks
2011-05-12T16:06:30Z

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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.

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