From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xJytk5J4szDrVT for ; Sat, 29 Jul 2017 05:03:58 +1000 (AEST) Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v6SJ2DMe004492 for ; Fri, 28 Jul 2017 15:03:56 -0400 Received: from e15.ny.us.ibm.com (e15.ny.us.ibm.com [129.33.205.205]) by mx0a-001b2d01.pphosted.com with ESMTP id 2c0709n2dd-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 28 Jul 2017 15:03:55 -0400 Received: from localhost by e15.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 28 Jul 2017 15:03:54 -0400 Date: Fri, 28 Jul 2017 12:03:50 -0700 From: "Paul E. McKenney" To: Jonathan Cameron Cc: dzickus@redhat.com, sfr@canb.auug.org.au, linuxarm@huawei.com, Nicholas Piggin , abdhalee@linux.vnet.ibm.com, sparclinux@vger.kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, David Miller , linux-arm-kernel@lists.infradead.org, tglx@linutronix.de Subject: Re: RCU lockup issues when CONFIG_SOFTLOCKUP_DETECTOR=n - any one else seeing this? Reply-To: paulmck@linux.vnet.ibm.com References: <20170727014214.GH3730@linux.vnet.ibm.com> <20170727143400.23e4d2b2@roar.ozlabs.ibm.com> <20170727124913.GL3730@linux.vnet.ibm.com> <20170727144903.000022a1@huawei.com> <20170727173923.000001b2@huawei.com> <20170727165245.GD3730@linux.vnet.ibm.com> <20170728084411.00001ddb@huawei.com> <20170728142403.0000122b@huawei.com> <20170728165529.GF3730@linux.vnet.ibm.com> <20170728182053.000072aa@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170728182053.000072aa@huawei.com> Message-Id: <20170728190349.GM3730@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, Jul 28, 2017 at 06:27:05PM +0100, Jonathan Cameron wrote: > On Fri, 28 Jul 2017 09:55:29 -0700 > "Paul E. McKenney" wrote: > > > On Fri, Jul 28, 2017 at 02:24:03PM +0100, Jonathan Cameron wrote: > > > On Fri, 28 Jul 2017 08:44:11 +0100 > > > Jonathan Cameron wrote: > > > > [ . . . ] > > > > > Ok. Some info. I disabled a few driver (usb and SAS) in the interest of having > > > fewer timer events. Issue became much easier to trigger (on some runs before > > > I could get tracing up and running) > > >e > > > So logs are large enough that pastebin doesn't like them - please shoet if > > >>e another timer period is of interest. > > > > > > https://pastebin.com/iUZDfQGM for the timer trace. > > > https://pastebin.com/3w1F7amH for dmesg. > > > > > > The relevant timeout on the RCU stall detector was 8 seconds. Event is > > > detected around 835. > > > > > > It's a lot of logs, so I haven't identified a smoking gun yet but there > > > may well be one in there. > > > > The dmesg says: > > > > rcu_preempt kthread starved for 2508 jiffies! g112 c111 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 > > > > So I look for "rcu_preempt" timer events and find these: > > > > rcu_preempt-9 [019] .... 827.579114: timer_init: timer=ffff8017d5fc7da0 > > rcu_preempt-9 [019] d..1 827.579115: timer_start: timer=ffff8017d5fc7da0 function=process_timeout > > > > Next look for "ffff8017d5fc7da0" and I don't find anything else. > It does show up off the bottom of what would fit in pastebin... > > rcu_preempt-9 [001] d..1 837.681077: timer_cancel: timer=ffff8017d5fc7da0 > rcu_preempt-9 [001] .... 837.681086: timer_init: timer=ffff8017d5fc7da0 > rcu_preempt-9 [001] d..1 837.681087: timer_start: timer=ffff8017d5fc7da0 function=process_timeout expires=4295101298 [timeout=1] cpu=1 idx=0 flags= Odd. I would expect an expiration... And ten seconds is way longer than the requested one jiffy! > > The timeout was one jiffy, and more than a second later, no expiration. > > Is it possible that this event was lost? I am not seeing any sign of > > this is the trace. > > > > I don't see any sign of CPU hotplug (and I test with lots of that in > > any case). > > > > The last time we saw something like this it was a timer HW/driver problem, > > but it is a bit hard to imagine such a problem affecting both ARM64 > > and SPARC. ;-) > Could be different issues, both of which were hidden by that lockup detector. > > There is an errata work around for the timers on this particular board. > I'm only vaguely aware of it, so may be unconnected. > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/clocksource/arm_arch_timer.c?h=v4.13-rc2&id=bb42ca47401010fc02901b5e8f79e40a26f208cb > > Seems unlikely though! + we've not yet seen it on the other chips that > errata effects (not that that means much). If you can reproduce quickly, might be worth trying anyway... Thanx, Paul > Jonathan > > > > > Thomas, any debugging suggestions? > > > > Thanx, Paul > > >