Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760561AbZADTlZ (ORCPT ); Sun, 4 Jan 2009 14:41:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756372AbZADTlR (ORCPT ); Sun, 4 Jan 2009 14:41:17 -0500 Received: from e6.ny.us.ibm.com ([32.97.182.146]:35254 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751921AbZADTlQ (ORCPT ); Sun, 4 Jan 2009 14:41:16 -0500 Date: Sun, 4 Jan 2009 11:41:11 -0800 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: dhaval@linux.vnet.ibm.com, jens.axboe@oracle.com, mingo@elte.hu, snakebyte@gmx.de, andi@firstfloor.org, akpm@linux-foundation.org, dvhltc@us.ibm.com, niv@us.ibm.com, rostedt@goodmis.org, tglx@linutronix.de, manfred@colorfullife.com Subject: [PATCH] Make treercu safe for suspend and resume Message-ID: <20090104194111.GA16398@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2180 Lines: 57 Hello! Kudos to both Dhaval Giani and Jens Axboe for finding a bug in treercu that causes warnings after suspend-resume cycles in Dhaval's case and during stress tests in Jens's case. It would also probably cause failures if heavily stressed. The solution, ironically enough, is to revert to rcupreempt's code for initializing the dynticks state. And the patch even results in smaller code -- so what was I thinking??? This is 2.6.29 material, given that people really do suspend and resume Linux these days. ;-) Located-by: Dhaval Giani Located-by: Jens Axboe Tested-by: Dhaval Giani Tested-by: Jens Axboe Signed-off-by: Paul E. McKenney --- rcutree.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index a342b03..e0a347f 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -79,7 +79,10 @@ struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state); DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); #ifdef CONFIG_NO_HZ -DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks); +DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { + .dynticks_nesting = 1, + .dynticks = 1, +}; #endif /* #ifdef CONFIG_NO_HZ */ static int blimit = 10; /* Maximum callbacks per softirq. */ @@ -1379,13 +1382,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp) static void __cpuinit rcu_online_cpu(int cpu) { -#ifdef CONFIG_NO_HZ - struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); - - rdtp->dynticks_nesting = 1; - rdtp->dynticks |= 1; /* need consecutive #s even for hotplug. */ - rdtp->dynticks_nmi = (rdtp->dynticks_nmi + 1) & ~0x1; -#endif /* #ifdef CONFIG_NO_HZ */ rcu_init_percpu_data(cpu, &rcu_state); rcu_init_percpu_data(cpu, &rcu_bh_state); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); -- 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/