From owner-freebsd-fs@freebsd.org Mon Jul 3 15:40:50 2017 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id DAD5C9E92B0; Mon, 3 Jul 2017 15:40:50 +0000 (UTC) (envelope-from ben.rubson@gmail.com) Received: from mail-wm0-x229.google.com (mail-wm0-x229.google.com [IPv6:2a00:1450:400c:c09::229]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 5CB4D74D26; Mon, 3 Jul 2017 15:40:50 +0000 (UTC) (envelope-from ben.rubson@gmail.com) Received: by mail-wm0-x229.google.com with SMTP id f67so59056430wmh.1; Mon, 03 Jul 2017 08:40:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:message-id:mime-version:subject:date:references:to:in-reply-to; bh=ovyVCvyhloMQ/jD0OLGq195wBHMNIKxKL28wsOoe6w0=; b=APPCfGF4zioKvH5abBgg8/dOUCpooS6J4C/jbBbnU9wk0xTzZriBf985lfPrdLH5GB R1eBbxa61k5No5/jaAA3b8Tt5KZ0NbXssmitLSikDCgqJ8KmQAuE81YYs2bp/4lLfJxq 2Tb/M3FbHPBZm5+BpTmofd6Hw5qD6F4pDqWMGTRriTUQ2+1yPFxTjRzv9u9P9slYivjz MPIMhqkNwRiSTBqUKfxTnIcqPQ4VF7rlLoYFlVKO2RhTppiXvR/rRxP6QjYoYBjapq4C wXKw7+lAbWRZbPnzRa/E8Ahp55j5BTQE3QUCCj9JPeELMmoPCwaKG8KK1HrRV7WQ5RXs Sy3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:message-id:mime-version:subject:date :references:to:in-reply-to; bh=ovyVCvyhloMQ/jD0OLGq195wBHMNIKxKL28wsOoe6w0=; b=mchFoACaKc7oSenWNngsEVH7rMPzDg77ZLQ7w2v00IpOyQwcQs4iAEdszbmrs5MdHs aSk+kwFX4fzLmSxWJDvLxPb+LuTkUPwrMCFgH3WbNd2LRtifhZvalZTDyKHzoA8UhFPk gvzcAa0qv8SrqlIPFBlIZp05vwoC/2/dqFC8f5rd6l8s5zvIyatnzocQoOi1HWJ6SFEF 3y6pn1Vx3ZZ2kz88p8bi8nldzJ0VV7bayAiX5JIqBwD/ZOz4gTRhB/hAyQXJK5nJjZbf dyrPTO/RYiRxPkqkxvt5Eqor6YX1hSGvObjwMMeBhkMajc/D0e26A1VwVLyZ5q4w2Y5s V6Sw== X-Gm-Message-State: AIVw113by322m85Njz0ur3EFHHtlRyX/EHzJBB2SsXerP5m0Me68PaCt t+htYiU76gfj9oiimxs= X-Received: by 10.28.184.87 with SMTP id i84mr7233612wmf.22.1499096448410; Mon, 03 Jul 2017 08:40:48 -0700 (PDT) Received: from ben.home (LFbn-1-11339-180.w2-15.abo.wanadoo.fr. [2.15.165.180]) by smtp.gmail.com with ESMTPSA id n71sm18817841wrb.62.2017.07.03.08.40.47 (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 03 Jul 2017 08:40:47 -0700 (PDT) From: Ben RUBSON Message-Id: Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: I/O to pool appears to be hung, panic ! Date: Mon, 3 Jul 2017 17:40:46 +0200 References: <20170629144334.1e283570@fabiankeil.de> <1F414ECE-1856-4EA3-A141-88B64703D4D6@gmail.com> To: Freebsd fs , freebsd-scsi In-Reply-To: X-Mailer: Apple Mail (2.3124) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.23 X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 03 Jul 2017 15:40:51 -0000 > On 03 Jul 2017, at 17:27, Edward Napierala wrote: >=20 > 2017-07-03 14:36 GMT+01:00 Ben RUBSON >: > > On 03 Jul 2017, at 13:10, Edward Napierala > wrote: > > > > 2017-07-03 10:07 GMT+01:00 Ben RUBSON >>: > > > > > On 29 Jun 2017, at 15:36, Ben RUBSON >> wrote: > > > > > >> On 29 Jun 2017, at 14:43, Fabian Keil = = >> wrote: > > > > > > Thank you for your feedback Fabian. > > > > > >> Ben RUBSON = >> wrote: > > >> > > >>> One of my servers did a kernel panic last night, giving the = following message : > > >>> panic: I/O to pool 'home' appears to be hung on vdev guid 122... = at '/dev/label/G23iscsi'. > > >> [...] > > >>> Here are some numbers regarding this disk, taken from the server = hosting the pool : > > >>> (unfortunately not from the iscsi target server) > > >>> https://s23.postimg.org/zd8jy9xaj/busydisk.png = = > > > >>> > > >>> We clearly see that suddendly, disk became 100% busy, meanwhile = CPU was almost idle. > > > > We also clearly see that 5 minutes later (02:09) disk seems to be = back but became 100% busy again, > > and that 16 minutes later (default vfs.zfs.deadman_synctime_ms), = panic occurred. > > > > >>> No error message at all on both servers. > > >> [...] > > >>> The only log I have is the following stacktrace taken from the = server console : > > >>> panic: I/O to pool 'home' appears to be hung on vdev guid 122... = at '/dev/label/G23iscsi'. > > >>> cpuid =3D 0 > > >>> KDB: stack backtrace: > > >>> #0 0xffffffff80b240f7 at kdb_backtrace+0x67 > > >>> #1 0xffffffff80ad9462 at vpanic+0x182 > > >>> #2 0xffffffff80ad92d3 at panic+0x43 > > >>> #3 0xffffffff82238fa7 at vdev_deadman+0x127 > > >>> #4 0xffffffff82238ec0 at vdev_deadman+0x40 > > >>> #5 0xffffffff82238ec0 at vdev_deadman+0x40 > > >>> #6 0xffffffff8222d0a6 at spa_deadman+0x86 > > >>> #7 0xffffffff80af32da at softclock_call_cc+0x18a > > >>> #8 0xffffffff80af3854 at softclock+0x94 > > >>> #9 0xffffffff80a9348f at intr_event_execute_handlers+0x20f > > >>> #10 0xffffffff80a936f6 at ithread_loop+0xc6 > > >>> #11 0xffffffff80a900d5 at fork_exit+0x85 > > >>> #12 0xffffffff80f846fe at fork_trampoline+0xe > > >>> Uptime: 92d2h47m6s > > >>> > > >>> I would have been pleased to make a dump available. > > >>> However, despite my (correct ?) configuration, server did not = dump : > > >>> (nevertheless, "sysctl debug.kdb.panic=3D1" make it to dump) > > >>> # grep ^dump /boot/loader.conf /etc/rc.conf > > >>> /boot/loader.conf:dumpdev=3D"/dev/mirror/swap" > > >>> /etc/rc.conf:dumpdev=3D"AUTO" > > >> > > >> You may want to look at the NOTES section in gmirror(8). > > > > > > Yes, I should already be OK (prefer algorithm set). > > > > > >>> I use default kernel, with a rebuilt zfs module : > > >>> # uname -v > > >>> FreeBSD 11.0-RELEASE-p8 #0: Wed Feb 22 06:12:04 UTC 2017 = root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC > > >>> > > >>> I use the following iSCSI configuration, which disconnects the = disks "as soon as" they are unavailable : > > >>> kern.iscsi.ping_timeout=3D5 > > >>> kern.iscsi.fail_on_disconnection=3D1 > > >>> kern.iscsi.iscsid_timeout=3D5 > > >>> > > >>> I then think disk was at least correctly reachable during these = 20 busy minutes. > > >>> > > >>> So, any idea why I could have faced this issue ? > > >> > > >> Is it possible that the system was under memory pressure? > > > > > > No I don't think it was : > > > https://s1.postimg.org/uvsebpyyn/busydisk2.png = = > > > > More than 2GB of available memory. > > > Swap not used (624kB). > > > ARC behaviour seems correct (anon increases because ZFS can't = actually write I think). > > > Regarding the pool itself, it was receiving data at 6MB/s, sending = around 30kB blocks to disks. > > > When disk went busy, throughput fell to some kB, with 128kB = blocks. > > > > > >> geli's use of malloc() is known to cause deadlocks under memory = pressure: > > >> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D209759 = = > > > >> > > >> Given that gmirror uses malloc() as well it probably has the same = issue. > > > > > > I don't use geli so I should not face this issue. > > > > > >>> I would have thought ZFS would have taken the busy device = offline, instead of raising a panic. > > >>> Perhaps it is already possible to make ZFS behave like this ? > > >> > > >> There's a tunable for this: vfs.zfs.deadman_enabled. > > >> If the panic is just a symptom of the deadlock it's unlikely > > >> to help though. > > > > > > I think this tunable should have prevented the server from having = raised a panic : > > > # sysctl -d vfs.zfs.deadman_enabled > > > vfs.zfs.deadman_enabled: Kernel panic on stalled ZFS I/O > > > # sysctl vfs.zfs.deadman_enabled > > > vfs.zfs.deadman_enabled: 1 > > > > > > But not sure how it would have behaved then... > > > (busy disk miraculously back to normal status, memory pressure due = to anon increasing...) > > > > I then think it would be nice, once vfs.zfs.deadman_synctime_ms has = expired, > > to be able to take the busy device offline instead of raising a = panic. > > Currently, disabling deadman will avoid the panic but will let the = device slowing down the pool. > > > > I still did not found the root cause of this issue, not sure I will, > > quite difficult actually with a stacktrace and some performance = graphs only :/ > > > > What exactly is the disk doing when that happens? What does "gstat" = say? If the iSCSI > > target is also FreeBSD, what does ctlstat say? >=20 > As shown on this graph made with gstat numbers from initiator : > https://s23.postimg.org/zd8jy9xaj/busydisk.png = > The disk is continuously writing 3 MBps before the issue happens. > When it occurs, response time increases to around 30 seconds (100% = busy), > and consequently disk throughput drops down to some kBps. > CPU stays at an almost fully idle level. >=20 > As shown here, no memory pressure : > https://s1.postimg.org/uvsebpyyn/busydisk2.png = = > >=20 > At the end of graphs' lines, panic is raised. >=20 > iSCSI target is also FreeBSD, unfortunately ctlstat was not running = during the issue occurred. > So numbers will be average since system startup (102 days ago). > I also do not have gstat numbers from this disk on target side > (to help finding if it's a hardware issue, a iSCSI issue or something = else). > I will think about collecting these numbers if ever issue occurs = again. >=20 > It's kind of hard to say something definitive at this point, but I = suspect it's a problem > at the target side. I got a report about something quite similar some = two years ago, > and it turned out to be a problem with a disk controller on the = target. Thank you for your feedback. I then : - enabled gstat collection on target, to also have numbers on target, = not only on initiator ; - enabled controller logging (dev.mps.0.debug_level=3D0x1B) ; - disabled deadman. We should be able to investigate further in case issue occurs again. Of course feel free to notify me in case you have other ideas ! Thank you again, Ben