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Date: Mon, 14 Oct 2013 11:05:08 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@kernel.org>,
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        Paul McKenney <paulmck@linux.vnet.ibm.com>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2
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On Sat, Oct 12, 2013 at 07:06:56PM +0200, Oleg Nesterov wrote:
> it even disables irqs, so this should always imply rcu_read_lock() with
> any implementation, 

Not so; I could make an RCU implementation that drives the state machine
from rcu_read_unlock(). Such an implementation doesn't need the
interrupt driven poll-state driver we currently have and could thus
subvert that assumption :-)

Then again, there's a good reason PaulMck didn't pick this
implementation.

> In fact I do not even understand why getaffinity() doesn't simply
> return ->cpus_allowed, but this is off-topic.

Yeah, me neither :-(, it always surprises me. But changing it is likely
to break stuff so there we are.