From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751635AbcF2RwM (ORCPT ); Wed, 29 Jun 2016 13:52:12 -0400 Received: from mail-it0-f68.google.com ([209.85.214.68]:36730 "EHLO mail-it0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751460AbcF2RwJ (ORCPT ); Wed, 29 Jun 2016 13:52:09 -0400 MIME-Version: 1.0 In-Reply-To: <20160629164415.GG4650@linux.vnet.ibm.com> References: <20160621064302.GA20635@js1304-P5Q-DELUXE> <20160621125406.GF3923@linux.vnet.ibm.com> <20160622005208.GB25106@js1304-P5Q-DELUXE> <20160622190859.GA1473@linux.vnet.ibm.com> <20160623004935.GA20752@linux.vnet.ibm.com> <20160623023756.GA30438@js1304-P5Q-DELUXE> <20160623024742.GD1473@linux.vnet.ibm.com> <20160623025329.GA13095@linux.vnet.ibm.com> <20160629164415.GG4650@linux.vnet.ibm.com> From: Geert Uytterhoeven Date: Wed, 29 Jun 2016 19:52:06 +0200 X-Google-Sender-Auth: EuTweAD7x8JbkwaXl4HIMiD9hM0 Message-ID: Subject: Re: Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab: lockless decision to grow cache) To: Paul McKenney Cc: Linux-Renesas , Andrew Morton , David Rientjes , "linux-kernel@vger.kernel.org" , Pekka Enberg , Linux MM , Jesper Dangaard Brouer , Joonsoo Kim , Christoph Lameter , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, On Wed, Jun 29, 2016 at 6:44 PM, Paul E. McKenney wrote: > On Wed, Jun 29, 2016 at 04:54:44PM +0200, Geert Uytterhoeven wrote: >> On Thu, Jun 23, 2016 at 4:53 AM, Paul E. McKenney >> wrote: >> > On Wed, Jun 22, 2016 at 07:47:42PM -0700, Paul E. McKenney wrote: > > [ . . . ] > >> > @@ -4720,11 +4720,18 @@ static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp) >> > pr_info(" "); >> > level = rnp->level; >> > } >> > - pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum); >> > + pr_cont("%d:%d/%#lx/%#lx ^%d ", rnp->grplo, rnp->grphi, >> > + rnp->qsmask, >> > + rnp->qsmaskinit | rnp->qsmaskinitnext, rnp->grpnum); >> > } >> > pr_cont("\n"); >> > } >> >> For me it always crashes during the 37th call of synchronize_sched() in >> setup_kmem_cache_node(), which is the first call after secondary CPU bring up. >> With your and my debug code, I get: >> >> CPU: Testing write buffer coherency: ok >> CPU0: thread -1, cpu 0, socket 0, mpidr 80000000 >> Setting up static identity map for 0x40100000 - 0x40100058 >> cnt = 36, sync >> CPU1: thread -1, cpu 1, socket 0, mpidr 80000001 >> Brought up 2 CPUs >> SMP: Total of 2 processors activated (2132.00 BogoMIPS). >> CPU: All CPU(s) started in SVC mode. >> rcu_node tree layout dump >> 0:1/0x0/0x3 ^0 > > Thank you for running this! > > OK, so RCU knows about both CPUs (the "0x3"), and the previous > grace period has seen quiescent states from both of them (the "0x0"). > That would indicate that your synchronize_sched() showed up when RCU was > idle, so it had to start a new grace period. It also rules out failure > modes where RCU thinks that there are more CPUs than really exist. > (Don't laugh, such things have really happened.) > >> devtmpfs: initialized >> VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 1 >> clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, >> max_idle_ns: 19112604462750000 ns >> >> I hope it helps. Thanks! > > I am going to guess that this was the first grace period since the second > CPU came online. When there only on CPU online, synchronize_sched() > is a no-op. > > OK, this showed some things that aren't a problem. What might the > problem be? > > o The grace-period kthread has not yet started. It -should- start > at early_initcall() time, but who knows? Adding code to print > out that kthread's task_struct address. > > o The grace-period kthread might not be responding to wakeups. > Checking this requires that a grace period be in progress, > so please put a call_rcu_sched() just before the call to > rcu_dump_rcu_node_tree(). (Sample code below.) Adding code > to my patch to print out more GP-kthread state as well. > > o One of the CPUs might not be responding to RCU. That -should- > result in an RCU CPU stall warning, so I will ignore this > possibility for the moment. > > That said, do you have some way to determine whether scheduling > clock interrupts are really happening? Without these interrupts, > no RCU CPU stall warnings. I believe there are no clocksources yet. The jiffies clocksource is the first clocksource found, and that happens after the first call to synchronize_sched(), cfr. my dmesg snippet above. In a working boot: # cat /sys/bus/clocksource/devices/clocksource0/available_clocksource e0180000.timer jiffies # cat /sys/bus/clocksource/devices/clocksource0/current_clocksource e0180000.timer > OK, that should be enough for the next phase, please see the end for the > patch. This patch applies on top of my previous one. > > Could you please set this up as follows? > > struct rcu_head rh; > > rcu_dump_rcu_node_tree(&rcu_sched_state); /* Initial state. */ > call_rcu(&rh, do_nothing_cb); I added an empty do_nothing_cb() for this: static void do_nothing_cb(struct rcu_head *rcu_head) { } According to the debugging technique "comment everything out until it boots", it now hangs in call_rcu(). > schedule_timeout_uninterruptible(5 * HZ); /* Or whatever delay. */ > rcu_dump_rcu_node_tree(&rcu_sched_state); /* GP state. */ > synchronize_sched(); /* Probably hangs. */ > rcu_barrier(); /* Drop RCU's references to rh before return. */ Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds