From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932810Ab3IYBnF (ORCPT ); Tue, 24 Sep 2013 21:43:05 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:41757 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757695Ab3IYBmz (ORCPT ); Tue, 24 Sep 2013 21:42:55 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 01/10] rcu: Improve grace-period start logic Date: Tue, 24 Sep 2013 18:42:30 -0700 Message-Id: <1380073359-31959-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <20130925014210.GA31690@linux.vnet.ibm.com> References: <20130925014210.GA31690@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13092501-0320-0000-0000-0000011DA9AA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" This commit improves grace-period start logic by checking ->gp_flags under the lock and by issuing a warning if a grace period is already in progress. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 32618b3..d679a52 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1297,7 +1297,7 @@ static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp) } /* - * Initialize a new grace period. + * Initialize a new grace period. Return 0 if no grace period required. */ static int rcu_gp_init(struct rcu_state *rsp) { @@ -1306,10 +1306,18 @@ static int rcu_gp_init(struct rcu_state *rsp) rcu_bind_gp_kthread(); raw_spin_lock_irq(&rnp->lock); + if (rsp->gp_flags == 0) { + /* Spurious wakeup, tell caller to go back to sleep. */ + raw_spin_unlock_irq(&rnp->lock); + return 0; + } rsp->gp_flags = 0; /* Clear all flags: New grace period. */ - if (rcu_gp_in_progress(rsp)) { - /* Grace period already in progress, don't start another. */ + if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) { + /* + * Grace period already in progress, don't start another. + * Not supposed to be able to happen. + */ raw_spin_unlock_irq(&rnp->lock); return 0; } @@ -1474,8 +1482,7 @@ static int __noreturn rcu_gp_kthread(void *arg) wait_event_interruptible(rsp->gp_wq, rsp->gp_flags & RCU_GP_FLAG_INIT); - if ((rsp->gp_flags & RCU_GP_FLAG_INIT) && - rcu_gp_init(rsp)) + if (rcu_gp_init(rsp)) break; cond_resched(); flush_signals(current); -- 1.8.1.5