Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks()

Peter Zijlstra
2010-04-01T16:36:31Z

On Thu, 2010-04-01 at 09:15 -0700, Paul E. McKenney wrote:
> > I don't understand. I thought the problem was that the locks were
> > taken inside an rcu critical section; switching to srcu would fix
> > that. But how is call_rcu_preempt() related? Grepping a bit, what
> > is call_rcu_preempt()? my tree doesn't have it.
>
> I believe that Peter is referring to the RCU implementation you get
> with CONFIG_TREE_PREEMPT_RCU, which currently depends on CONFIG_PREEMPT.
> The other implementation is CONFIG_TREE_RCU, which is usually called
> "classic RCU".

Right, so I've been nudging Paul a while to make it so that we always
have preemptible rcu available and that only the default interface
switches between sched/classic and preempt.

Currently we already have:

call_rcu_sched()
call_rcu_bh()
call_rcu() (depends on CONFIG_PREEMPT_RCU)

I'm saying it would be nice to also have:

call_rcu_preempt()