From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751566AbcGNTU1 (ORCPT ); Thu, 14 Jul 2016 15:20:27 -0400 Received: from merlin.infradead.org ([205.233.59.134]:46518 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751113AbcGNTUZ (ORCPT ); Thu, 14 Jul 2016 15:20:25 -0400 Date: Thu, 14 Jul 2016 21:20:18 +0200 From: Peter Zijlstra To: Oleg Nesterov Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, tj@kernel.org, paulmck@linux.vnet.ibm.com, john.stultz@linaro.org, dimitrysh@google.com, romlem@google.com, ccross@google.com, tkjos@google.com Subject: Re: [PATCH 2/2] locking/percpu-rwsem: Introduce bias knob Message-ID: <20160714192018.GM30154@twins.programming.kicks-ass.net> References: <20160714182545.786693675@infradead.org> <20160714183022.336211504@infradead.org> <20160714184351.GA18388@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160714184351.GA18388@redhat.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 14, 2016 at 08:43:51PM +0200, Oleg Nesterov wrote: > > Oh well... I personally do not think this is what we want... Can't > we just add the stupid rcu_sync_enter() into cgroup_init() at least > for now? Yes, this means the unnecessary .sync() at boot time, but > it will go away after cleanups I am going to send. Something like so then? --- --- a/include/linux/rcu_sync.h +++ b/include/linux/rcu_sync.h @@ -59,6 +59,7 @@ static inline bool rcu_sync_is_idle(stru } extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type); +extern void rcu_sync_sabotage(struct rcu_sync *); extern void rcu_sync_enter(struct rcu_sync *); extern void rcu_sync_exit(struct rcu_sync *); extern void rcu_sync_dtor(struct rcu_sync *); --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -5609,6 +5609,8 @@ int __init cgroup_init(void) BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files)); BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files)); + rcu_sync_sabotage(&cgroup_threadgroup_rwsem.rss); + get_user_ns(init_cgroup_ns.user_ns); mutex_lock(&cgroup_mutex); --- a/kernel/rcu/sync.c +++ b/kernel/rcu/sync.c @@ -83,6 +83,21 @@ void rcu_sync_init(struct rcu_sync *rsp, } /** + * rcu_sync_sabotage() - Sabotage a fresh rcu_sync instance + * @rsp: Pointer to rcu_sync structure to be sabotaged + * + * Must be called after rcu_sync_init() and before first use. + * + * Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}() pairs + * turn into NO-OPs. + */ +void rcu_sync_sabotage(struct rcu_sync *rsp) +{ + rsp->gp_count++; + rsp->gp_state = !GP_IDLE; +} + +/** * rcu_sync_enter() - Force readers onto slowpath * @rsp: Pointer to rcu_sync structure to use for synchronization *