From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-x241.google.com (mail-pf0-x241.google.com [IPv6:2607:f8b0:400e:c00::241]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xHzdm4k44zDrFD for ; Thu, 27 Jul 2017 14:34:20 +1000 (AEST) Received: by mail-pf0-x241.google.com with SMTP id y25so9726406pfk.4 for ; Wed, 26 Jul 2017 21:34:20 -0700 (PDT) Date: Thu, 27 Jul 2017 14:34:00 +1000 From: Nicholas Piggin To: "Paul E. McKenney" Cc: David Miller , Jonathan.Cameron@huawei.com, dzickus@redhat.com, sfr@canb.auug.org.au, linuxarm@huawei.com, abdhalee@linux.vnet.ibm.com, sparclinux@vger.kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org Subject: Re: RCU lockup issues when CONFIG_SOFTLOCKUP_DETECTOR=n - any one else seeing this? Message-ID: <20170727143400.23e4d2b2@roar.ozlabs.ibm.com> In-Reply-To: <20170727014214.GH3730@linux.vnet.ibm.com> References: <20170726223658.GA27617@linux.vnet.ibm.com> <20170726.154540.150558937277891719.davem@davemloft.net> <20170726231505.GG3730@linux.vnet.ibm.com> <20170726.162200.1904949371593276937.davem@davemloft.net> <20170727014214.GH3730@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 26 Jul 2017 18:42:14 -0700 "Paul E. McKenney" wrote: > On Wed, Jul 26, 2017 at 04:22:00PM -0700, David Miller wrote: > > Indeed, that really wouldn't explain how we end up with a RCU stall > > dump listing almost all of the cpus as having missed a grace period. > > I have seen stranger things, but admittedly not often. So the backtraces show the RCU gp thread in schedule_timeout. Are you sure that it's timeout has expired and it's not being scheduled, or could it be a bad (large) timeout (looks unlikely) or that it's being scheduled but not correctly noting gps on other CPUs? It's not in R state, so if it's not being scheduled at all, then it's because the timer has not fired: [ 1984.628602] rcu_preempt kthread starved for 5663 jiffies! g1566 c1565 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 [ 1984.638153] rcu_preempt S 0 9 2 0x00000000 [ 1984.643626] Call trace: [ 1984.646059] [] __switch_to+0x90/0xa8 [ 1984.651189] [] __schedule+0x19c/0x5d8 [ 1984.656400] [] schedule+0x38/0xa0 [ 1984.661266] [] schedule_timeout+0x124/0x218 [ 1984.667002] [] rcu_gp_kthread+0x4fc/0x748 [ 1984.672564] [] kthread+0xfc/0x128 [ 1984.677429] [] ret_from_fork+0x10/0x50