From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751504AbdAPQoU (ORCPT ); Mon, 16 Jan 2017 11:44:20 -0500 Received: from merlin.infradead.org ([205.233.59.134]:40164 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751402AbdAPQnz (ORCPT ); Mon, 16 Jan 2017 11:43:55 -0500 Date: Mon, 16 Jan 2017 17:43:37 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations Message-ID: <20170116164337.GB6500@twins.programming.kicks-ass.net> References: <20170114085406.GA19052@linux.vnet.ibm.com> <1484384085-19444-3-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1484384085-19444-3-git-send-email-paulmck@linux.vnet.ibm.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 Sat, Jan 14, 2017 at 12:54:42AM -0800, Paul E. McKenney wrote: > /* > + * Record entry into an extended quiescent state. This is only to be > + * called when not already in an extended quiescent state. > + */ > +static void rcu_dynticks_eqs_enter(void) > +{ > + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > + > + /* > + * CPUs seeing atomic_inc() must see prior RCU read-side critical > + * sections, and we also must force ordering with the next idle > + * sojourn. > + */ > + smp_mb__before_atomic(); /* See above. */ > + atomic_inc(&rdtp->dynticks); > + smp_mb__after_atomic(); /* See above. */ > + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && > + atomic_read(&rdtp->dynticks) & 0x1); > +} In an earlier patch you replaced things with atomic_add_return(), why not use atomic_inc_return() here?