Subject: Re: [PATCH v2] net IPv6 : Fix broken IPv6 routing table after loopback down-up

From: "Paul E. McKenney" <[email-masked]>
Date: Thu, 28 Mar 2013 12:39:57 -0700

On Thu, Mar 28, 2013 at 11:49:37AM -0700, Eric Dumazet wrote:
> On Thu, 2013-03-28 at 11:23 -0700, Paul E. McKenney wrote:
> 
> > 
> > Agreed, there is no point in using RCU when it is not needed.
> > 
> > That said...
> > 
> > Since v3.1, in CONFIG_PREEMPT=y kernels, rcu_read_lock() does not
> > disable preemption.  In CONFIG_PREEMPT=n kernels, rcu_read_lock() does
> > disable preemption, but to no effect because preemption is already
> > disabled anyway.
> > 
> > The net effect is that rcu_read_lock() has no effect on preemption.
> > 
> 
> Good point, but this patch might be a stable candidate.
> 
> Rule of thumb for networking is 
> 
> 1) Control path : RTNL mutex
> 
> 2) Data path : RTNL cant be taken (from softirq), so use RCU if
> possible.

Stable candidate and rules of thumb sound good to me!

							Thanx, Paul