Date: Thu, 29 Jun 2017 15:36:45 +0200 From: Ben RUBSON <ben.rubson@gmail.com> To: Freebsd fs <freebsd-fs@freebsd.org>, freebsd-scsi@freebsd.org Subject: Re: I/O to pool appears to be hung, panic ! Message-ID: <A1CC7D73-4196-4503-9716-52E84AA24FD3@gmail.com> In-Reply-To: <20170629144334.1e283570@fabiankeil.de> References: <E8CC223E-3F41-4036-84A9-FBA693AC2CAA@gmail.com> <20170629144334.1e283570@fabiankeil.de>
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> On 29 Jun 2017, at 14:43, Fabian Keil <freebsd-listen@fabiankeil.de> = wrote: Thank you for your feedback Fabian. > Ben RUBSON <ben.rubson@gmail.com> wrote: >=20 >> 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'. > [...]=20 >> 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 >>=20 >> We clearly see that suddendly, disk became 100% busy, meanwhile CPU = was almost idle. >>=20 >> 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 >>=20 >> 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" >=20 > 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=20 >>=20 >> 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 >>=20 >> I then think disk was at least correctly reachable during these 20 = busy minutes. >>=20 >> So, any idea why I could have faced this issue ? >=20 > 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 >=20 > 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 ? >=20 > 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 also tried to look for some LSI SAS2008 error counters (on target = side), but did not found anything interesting. (sysctl -a | grep -i mps) Thank you again, Ben
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