From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751222Ab2IZEez (ORCPT ); Wed, 26 Sep 2012 00:34:55 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:41038 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750772Ab2IZEex (ORCPT ); Wed, 26 Sep 2012 00:34:53 -0400 Date: Tue, 25 Sep 2012 21:34:45 -0700 From: "Paul E. McKenney" To: Fengguang Wu Cc: Josh Boyer , Christian Hoffmann , LKML Subject: Re: INFO: rcu_preempt detected stalls on CPUs/tasks: { 1} (detected by 0, t=10002 jiffies) Message-ID: <20120926043445.GB2524@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120925111938.GA4545@localhost> <20120925150701.GA2502@linux.vnet.ibm.com> <20120926042237.GA18287@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120926042237.GA18287@localhost> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12092604-2876-0000-0000-0000007DBA8B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 26, 2012 at 12:22:37PM +0800, Fengguang Wu wrote: > On Tue, Sep 25, 2012 at 08:07:01AM -0700, Paul E. McKenney wrote: > > On Tue, Sep 25, 2012 at 07:19:38PM +0800, Fengguang Wu wrote: > > > Hi Paul, > > > > > > I've just bisected down one RCU stall problem: > > > > > > [ 12.035785] pktgen: Packet Generator for packet performance testing. Version: 2.74 > > > [ 12.435439] atkbd: probe of serio0 rejects match -19 > > > [ 111.700160] INFO: rcu_preempt detected stalls on CPUs/tasks: { 1} (detected by 0, t=10002 jiffies) > > > [ 111.700171] Pid: 0, comm: swapper/0 Not tainted 3.6.0-rc5-00004-gda10491 #1 > > > [ 111.700178] Call Trace: > > > [ 111.700475] [] rcu_check_callbacks+0x544/0x570 > > > [ 111.700538] [] update_process_times+0x36/0x70 > > > [ 111.700547] [] tick_sched_timer+0x57/0xc0 > > > [ 111.700552] [] __run_hrtimer.isra.31+0x4a/0xc0 > > > [ 111.700557] [] ? tick_nohz_handler+0xf0/0xf0 > > > [ 111.700559] [] hrtimer_interrupt+0xf5/0x290 > > > [ 111.700562] [] ? sched_clock_idle_wakeup_event+0x18/0x20 > > > [ 111.700565] [] ? tick_nohz_stop_idle+0x39/0x40 > > > [ 111.700572] [] smp_apic_timer_interrupt+0x4f/0x80 > > > [ 111.700587] [] apic_timer_interrupt+0x2a/0x30 > > > [ 111.700593] [] ? native_safe_halt+0x5/0x10 > > > [ 111.700599] [] default_idle+0x29/0x50 > > > [ 111.700601] [] cpu_idle+0x68/0xb0 > > > [ 111.700609] [] rest_init+0x67/0x70 > > > [ 111.700627] [] start_kernel+0x2ea/0x2f0 > > > [ 111.700629] [] ? repair_env_string+0x51/0x51 > > > [ 111.700631] [] i386_start_kernel+0x78/0x7d > > > [ 127.040302] bus: 'serio': driver_probe_device: matched device serio0 with driver atkbd > > > [ 127.041308] CPA self-test: > > > > > > to this commit: > > > > > > commit 06ae115a1d551cd952d80df06eaf8b5153351875 > > > Author: Paul E. McKenney > > > Date: Sun Aug 14 15:56:54 2011 -0700 > > > > > > rcu: Avoid having just-onlined CPU resched itself when RCU is idle > > > > Interesting. Of course the stack is from the CPU that detected the > > problem rather than the problematic CPU. ;-) > > > > Could you please try the following patch? > > Paul, thanks for the quick fix! However it may still stall sometimes. > Attached are 3 dmesgs with the stalls. Do you have c96ea7cf from -rcu applied? Corresponding patch is below. Thanx, Paul ------------------------------------------------------------------------ rcu: Avoid spurious RCU CPU stall warnings If a given CPU avoids the idle loop but also avoids starting a new RCU grace period for a full minute, RCU can issue spurious RCU CPU stall warnings. This commit fixes this issue by adding a check for ongoing grace period to avoid these spurious stall warnings. Reported-by: Becky Bruce Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 2cf8eb3..98f2752 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -819,7 +819,8 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) j = ACCESS_ONCE(jiffies); js = ACCESS_ONCE(rsp->jiffies_stall); rnp = rdp->mynode; - if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) { + if (rcu_gp_in_progress(rsp) && + (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp);