Re: [PATCH] netfilter: use per-cpu recursive lock (v11)

Evgeniy Polyakov
2009-04-21T08:17:19Z

Hi.

On Tue, Apr 21, 2009 at 02:52:30PM +0800, Lai Jiangshan (laijs@cn.fujitsu.com) wrote:
> > +void xt_info_rdlock_bh(void)
> > > +{
> > > + struct xt_info_lock *lock;
> > > +
> > > + preempt_disable();
> > > + lock = &__get_cpu_var(xt_info_locks);
> > > + if (likely(++lock->depth == 0))
>
> So what happen when xt_info_rdlock_bh() called recursively here?
>
> > > + spin_lock_bh(&lock->lock);
> > > + preempt_enable_no_resched();
> > > +}
> > > +EXPORT_SYMBOL_GPL(xt_info_rdlock_bh);
> > > +
>
> ----------
> Is this OK? (Now I suppose we can enter the read-side critical region
> in irq context)
>
> void xt_info_rdlock_bh(void)
> {
> unsigned long flags;
> struct xt_info_lock *lock;
>
> local_irq_save(flags);
> lock = &__get_cpu_var(xt_info_locks);
> if (likely(++lock->depth == 0))
> spin_lock_bh(&lock->lock);
> local_irq_restore(flags);
> }

Netfilter as long as other generic network pathes are never accessed
from interrupt context, but your analysis looks right for the softirq
case.

Stephen, should preempt_disable() be replaced with local_bh_disable() to
prevent softirq to race on the same cpu for the lock's depth field? Or
can it be made atomic?

--
Evgeniy Polyakov