Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to prevent CPU offline

From: "Paul E. McKenney" <[email-masked]>
Date: Wed, 26 Jun 2013 07:34:24 -0700

On Wed, Jun 26, 2013 at 03:29:40PM +0100, David Laight wrote:
> > Once stop_machine() is gone from the CPU offline path, we won't be able
> > to depend on disabling preemption to prevent CPUs from going offline
> > from under us.
> 
> Could you use an rcu-like sequence so that disabling pre-emption
> would be enough?
> 
> Something like rebuilding the cpu list, then forcing yourself
> to run on all the cpu.
> 
> That would be far less intrusive.

It would also increase the latency of CPU-hotunplug operations.

							Thanx, Paul