linux-kernel - Re: [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging normal ones

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Message-ID: <20150701101221.GS19282@twins.programming.kicks-ass.net>
Date:	Wed, 1 Jul 2015 12:12:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
	oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging
 normal ones

On Tue, Jun 30, 2015 at 08:37:01PM -0700, Paul E. McKenney wrote:
> > Wait, what?  Why is anything using traditional (non-S) RCU while *any*
> > lock is held?
> 
> In their defense, it is a sleeplock that is never taken except when
> rearranging networking configuration.  Sometimes they need a grace period
> under the lock.  So synchronize_net() checks to see if RTNL is held, and
> does a synchronize_rcu_expedited() if so and a synchronize_rcu() if not.

Sounds vile.
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