Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753891AbbGANmB (ORCPT ); Wed, 1 Jul 2015 09:42:01 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:51114 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752304AbbGANlx (ORCPT ); Wed, 1 Jul 2015 09:41:53 -0400 X-Helo: d03dlp03.boulder.ibm.com X-MailFrom: paulmck@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Date: Wed, 1 Jul 2015 06:41:44 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.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 RFC tip/core/rcu 2/5] rcu: Short-circuit normal GPs via expedited GPs Message-ID: <20150701134143.GY3717@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20150630214805.GA7795@linux.vnet.ibm.com> <1435700910-9104-1-git-send-email-paulmck@linux.vnet.ibm.com> <1435700910-9104-2-git-send-email-paulmck@linux.vnet.ibm.com> <20150701100521.GP19282@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150701100521.GP19282@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15070113-0005-0000-0000-0000133C21B2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1042 Lines: 26 On Wed, Jul 01, 2015 at 12:05:21PM +0200, Peter Zijlstra wrote: > On Tue, Jun 30, 2015 at 02:48:27PM -0700, Paul E. McKenney wrote: > > rsp->gp_state = RCU_GP_WAIT_FQS; > > ret = wait_event_interruptible_timeout(rsp->gp_wq, > > + ((gf = READ_ONCE(rsp->gp_flags)) & > > + RCU_GP_FLAG_FQS) || > > + (!READ_ONCE(rnp->qsmask) && > > + !rcu_preempt_blocked_readers_cgp(rnp)) || > > + rcu_exp_gp_seq_done(rsp->exp_rsp, > > + rsp->gp_exp_snap), > > + j); > > rsp->gp_state = RCU_GP_DONE_FQS; > > How can the GP be done if we timed out or got interrupted? If all the CPUs still blocking the grace period went idle, or in a NO_HZ_FULL kernel, entered nohz_full userspace execution. Or, if certain low-probability races happen, went offline. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/