From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f69.google.com (mail-it0-f69.google.com [209.85.214.69]) by kanga.kvack.org (Postfix) with ESMTP id 92893828E1 for ; Thu, 30 Jun 2016 03:58:53 -0400 (EDT) Received: by mail-it0-f69.google.com with SMTP id g127so144969134ith.3 for ; Thu, 30 Jun 2016 00:58:53 -0700 (PDT) Received: from mail-it0-x244.google.com (mail-it0-x244.google.com. [2607:f8b0:4001:c0b::244]) by mx.google.com with ESMTPS id w63si302074ith.8.2016.06.30.00.58.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 Jun 2016 00:58:52 -0700 (PDT) Received: by mail-it0-x244.google.com with SMTP id h190so8201286ith.3 for ; Thu, 30 Jun 2016 00:58:52 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160630074710.GC30114@js1304-P5Q-DELUXE> References: <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> <20160629181208.GP4650@linux.vnet.ibm.com> <20160630074710.GC30114@js1304-P5Q-DELUXE> From: Geert Uytterhoeven Date: Thu, 30 Jun 2016 09:58:51 +0200 Message-ID: Subject: Re: Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab: lockless decision to grow cache) Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: "Paul E. McKenney" , Linux-Renesas , Andrew Morton , David Rientjes , "linux-kernel@vger.kernel.org" , Pekka Enberg , Linux MM , Jesper Dangaard Brouer , Christoph Lameter , "linux-arm-kernel@lists.infradead.org" Hi Joonsoo, On Thu, Jun 30, 2016 at 9:47 AM, Joonsoo Kim wrote: > On Wed, Jun 29, 2016 at 11:12:08AM -0700, Paul E. McKenney wrote: >> On Wed, Jun 29, 2016 at 07:52:06PM +0200, Geert Uytterhoeven wrote: >> > 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 >> >> Ah! But if there is no jiffies clocksource, then schedule_timeout() >> and friends will never return, correct? If so, I guarantee you that >> synchronize_sched() will unconditionally hang. >> >> So if I understand correctly, the fix is to get the jiffies clocksource >> running before the first call to synchronize_sched(). > > If so, following change would be sufficient. > > Thanks. > > ------>8------- > diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c > index 555e21f..4f6471f 100644 > --- a/kernel/time/jiffies.c > +++ b/kernel/time/jiffies.c > @@ -98,7 +98,7 @@ static int __init init_jiffies_clocksource(void) > return __clocksource_register(&clocksource_jiffies); > } > > -core_initcall(init_jiffies_clocksource); > +early_initcall(init_jiffies_clocksource); > > struct clocksource * __init __weak clocksource_default_clock(void) > { Thanks for your patch! While this does move jiffies clocksource initialization before secondary CPU bringup, it still hangs when calling call_rcu() or synchronize_sched(): 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 clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns 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: rcu_sched GP kthread: c784e1c0 state: 1 flags: 0x0 g:-300 c:-300 jiffies: 0xffff8ad0 GP start: 0x0 Last GP activity: 0x0 rcu_node tree layout dump 0:1/0x0/0x3 ^0 devtmpfs: initialized VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 1 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org