From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752755AbaGWM0P (ORCPT ); Wed, 23 Jul 2014 08:26:15 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:40288 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750787AbaGWM0O (ORCPT ); Wed, 23 Jul 2014 08:26:14 -0400 Date: Wed, 23 Jul 2014 05:26:08 -0700 From: "Paul E. McKenney" To: Pranith Kumar Cc: Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , "open list:READ-COPY UPDATE..." Subject: Re: [PATCH 11/16] rcu: Check for spurious wakeup using return value Message-ID: <20140723122608.GL11241@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1406092194-13004-1-git-send-email-bobby.prani@gmail.com> <1406092194-13004-12-git-send-email-bobby.prani@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1406092194-13004-12-git-send-email-bobby.prani@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14072312-6688-0000-0000-0000037FB96C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 23, 2014 at 01:09:48AM -0400, Pranith Kumar wrote: > When the gp_kthread wakes up from the wait event, it returns 0 if the wake up is > due to the condition having been met. This commit checks this return value > for a spurious wake up before calling rcu_gp_init(). > > Signed-off-by: Pranith Kumar How does this added check help? I don't see that it does. If the flag is set, we want to wake up. If we get a spurious wakeup, but then the flag gets set before we actually wake up, we still want to wake up. So sorry, but no. Thanx, Paul PS. BTW, the ones that I am not immediately responding to are those that I will recheck later on and possibly accept. > --- > kernel/rcu/tree.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index f8847d9..3b20ad2 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1790,11 +1790,11 @@ static int __noreturn rcu_gp_kthread(void *arg) > ACCESS_ONCE(rsp->gpnum), > TPS("reqwait")); > rsp->gp_state = RCU_GP_WAIT_GPS; > - wait_event_interruptible(rsp->gp_wq, > + ret = wait_event_interruptible(rsp->gp_wq, > ACCESS_ONCE(rsp->gp_flags) & > RCU_GP_FLAG_INIT); > /* Locking provides needed memory barrier. */ > - if (rcu_gp_init(rsp)) > + if (!ret && rcu_gp_init(rsp)) > break; > cond_resched(); > flush_signals(current); > -- > 2.0.0.rc2 >