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Violators will be prosecuted for from ; Thu, 30 Jun 2016 09:24:01 -0400 Received: from b01cxnp23033.gho.pok.ibm.com (b01cxnp23033.gho.pok.ibm.com [9.57.198.28]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id 38C1A6E803C for ; Thu, 30 Jun 2016 09:23:41 -0400 (EDT) Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by b01cxnp23033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u5UDO0ag41025670 for ; Thu, 30 Jun 2016 13:24:00 GMT Received: from d01av01.pok.ibm.com (localhost [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u5UDNxOQ017177 for ; Thu, 30 Jun 2016 09:23:59 -0400 Date: Thu, 30 Jun 2016 06:24:01 -0700 From: "Paul E. McKenney" Subject: Re: Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab: lockless decision to grow cache) Reply-To: paulmck@linux.vnet.ibm.com References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20160630132401.GT4650@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Geert Uytterhoeven Cc: Joonsoo Kim , 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" On Thu, Jun 30, 2016 at 09:58:51AM +0200, Geert Uytterhoeven wrote: > 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 This is in fact the initial state for RCU grace periods. In other words, all the earlier calls to synchronize_sched() likely happened while there was only one CPU online. > devtmpfs: initialized > VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 1 Could you please add the call_rcu() and timed delay as described in my earlier email? That would hopefully help me see the state of the stalled grace period. Thanx, Paul > 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