On Thu, Jul 26, 2018 at 5:15 PM Alex Gorbachev <ag@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, Jul 26, 2018 at 9:49 AM, Ilya Dryomov <idryomov@xxxxxxxxx> wrote:
> > On Thu, Jul 26, 2018 at 1:07 AM Alex Gorbachev <ag@xxxxxxxxxxxxxxxxxxx> wrote:
> >>
> >> On Wed, Jul 25, 2018 at 6:07 PM, Alex Gorbachev <ag@xxxxxxxxxxxxxxxxxxx> wrote:
> >> > On Wed, Jul 25, 2018 at 5:51 PM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
> >> >>
> >> >>
> >> >> On Wed, Jul 25, 2018 at 5:41 PM Alex Gorbachev <ag@xxxxxxxxxxxxxxxxxxx>
> >> >> wrote:
> >> >>>
> >> >>> I am not sure this related to RBD, but in case it is, this would be an
> >> >>> important bug to fix.
> >> >>>
> >> >>> Running LVM on top of RBD, XFS filesystem on top of that, consumed in RHEL
> >> >>> 7.4.
> >> >>>
> >> >>> When running a large read operation and doing LVM snapshots during
> >> >>> that operation, the block being read winds up all zeroes in pagecache.
> >> >>>
> >> >>> Dropping the caches syncs up the block with what's on "disk" and
> >> >>> everything is fine.
> >> >>>
> >> >>> Working on steps to reproduce simply - ceph is Luminous 12.2.7, RHEL
> >> >>> client is Jewel 10.2.10-17.el7cp
> >> >>
> >> >>
> >> >> Is this krbd or QEMU+librbd? If the former, what kernel version are you
> >> >> running?
> >> >
> >> > It's krbd on RHEL.
> >> >
> >> > RHEL kernel:
> >> >
> >> > Linux dmg-cbcache01 3.10.0-862.el7.x86_64 #1 SMP Wed Mar 21 18:14:51
> >> > EDT 2018 x86_64 x86_64 x86_64 GNU/Linux
> >>
> >> Not sure if this is exactly replicating the issue, but I was able to
> >> do this on two different systems:
> >>
> >> RHEL 7.4 kernel as above.
> >
> > 3.10.0-862.el7 is a RHEL 7.5 kernel.
> > I think you have a 7.4 system with a 7.5 kernel.
>
> I was wrong, it's 7.5:
>
> Red Hat Enterprise Linux Server release 7.5 (Maipo)
>
> >
> >>
> >> Create a PVM PV on a mapped kRBD device
> >>
> >> example: pvcreate /dev/rbd/spin1/lvm1
> >>
> >> Create a VG and LV, make an XFS FS
> >>
> >> vgcreate datavg /dev/rbd/spin1/lvm1
> >> lvcreate -n data1 -L 5G datavg
> >> mkfs.xfs /dev/datavg/data1
> >> <mount on something>
> >>
> >> Get some large file and copy it to some other file, same storage or
> >> different. All is well.
> >
> > Same storage as in the same XFS filesystem? Is copying it from
> > /mnt/foo to /mnt/bar enough (assuming /dev/datavg/data1 is on /mnt)?
>
> I tried both same and different. Yes, copy on the same fs appears to
> be enough to trigger this.
>
> >
> >>
> >> Now snapshot the LV
> >>
> >> lvcreate -l8%ORIGIN -s -n snap_data1 /dev/datavg/data1 --addtag backup
> >
> > 8% of 5G is 400M. How large is the file?
>
> This is just an example, I tried it with a 94 GB filesystem and a 5GB
> file, and also with a 700gb VG and a 70 GB filesystem and a 10 GB file
>
> >
> >>
> >> Now try to copy that file again. I get:
> >>
> >> NMI watchdog: BUG: soft lockup - CPU#2 stuck for 22s! [kworker/2:1:3470]
> >>
> >> And in dmesg (this is on Proxmox but I did the same on ESXi)
> >>
> >> [1397609.308673] sched: RT throttling activated
> >> [1397658.759259] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 23s!
> >> [kworker/0:1:2648]
> >> [1397658.759354] Modules linked in: dm_snapshot dm_bufio rbd libceph
> >> rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace fscache
> >> sunrpc ppdev joydev pcspkr sg parport_pc virtio_balloon parport shpchp
> >> i2c_piix4 ip_tables xfs libcrc32c sd_mod sr_mod crc_t10dif
> >> crct10dif_generic cdrom crct10dif_common ata_generic pata_acpi
> >> virtio_scsi virtio_console virtio_net bochs_drm drm_kms_helper
> >> syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm ata_piix libata
> >> serio_raw virtio_pci i2c_core virtio_ring virtio floppy dm_mirror
> >> dm_region_hash dm_log dm_mod
> >> [1397658.759400] CPU: 0 PID: 2648 Comm: kworker/0:1 Kdump: loaded Not
> >> tainted 3.10.0-862.el7.x86_64 #1
> >> [1397658.759402] Hardware name: QEMU Standard PC (i440FX + PIIX,
> >> 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org
> >> 04/01/2014
> >> [1397658.759415] Workqueue: kcopyd do_work [dm_mod]
> >> [1397658.759418] task: ffff932df65d3f40 ti: ffff932fb138c000 task.ti:
> >> ffff932fb138c000
> >> [1397658.759420] RIP: 0010:[<ffffffffc08535a0>] [<ffffffffc08535a0>]
> >> copy_callback+0x50/0x130 [dm_snapshot]
> >> [1397658.759426] RSP: 0018:ffff932fb138fd08 EFLAGS: 00000283
> >> [1397658.759428] RAX: 000000000003e5e8 RBX: ffffebecc4943ec0 RCX:
> >> ffff932ff4704068
> >> [1397658.759430] RDX: ffff932dc8050d00 RSI: ffff932fd6a0f9b8 RDI:
> >> 0000000000000000
> >> [1397658.759431] RBP: ffff932fb138fd28 R08: ffff932dc7d2c0b0 R09:
> >> ffff932dc8050d20
> >> [1397658.759433] R10: 00000000c7d2b301 R11: ffffebecc01f4a00 R12:
> >> 0000000000000000
> >> [1397658.759435] R13: 0000000180090003 R14: 0000000000000000 R15:
> >> 00000000ffffff80
> >> [1397658.759438] FS: 0000000000000000(0000) GS:ffff932fffc00000(0000)
> >> knlGS:0000000000000000
> >> [1397658.759440] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> >> [1397658.759442] CR2: 00007f17bcd5e860 CR3: 0000000042c0e000 CR4:
> >> 00000000000006f0
> >> [1397658.759447] Call Trace:
> >> [1397658.759452] [<ffffffffc0853550>] ? origin_resume+0x70/0x70 [dm_snapshot]
> >> [1397658.759459] [<ffffffffc0340eab>] run_complete_job+0x6b/0xc0 [dm_mod]
> >> [1397658.759466] [<ffffffffc0340f60>] process_jobs+0x60/0x100 [dm_mod]
> >> [1397658.759471] [<ffffffffc0340e40>] ? kcopyd_put_pages+0x50/0x50 [dm_mod]
> >> [1397658.759477] [<ffffffffc0341042>] do_work+0x42/0x90 [dm_mod]
> >> [1397658.759483] [<ffffffffa08b2dff>] process_one_work+0x17f/0x440
> >> [1397658.759485] [<ffffffffa08b3bcc>] worker_thread+0x22c/0x3c0
> >> [1397658.759489] [<ffffffffa08b39a0>] ? manage_workers.isra.24+0x2a0/0x2a0
> >> [1397658.759494] [<ffffffffa08bae31>] kthread+0xd1/0xe0
> >> [1397658.759497] [<ffffffffa08bad60>] ? insert_kthread_work+0x40/0x40
> >> [1397658.759503] [<ffffffffa0f1f637>] ret_from_fork_nospec_begin+0x21/0x21
> >> [1397658.759506] [<ffffffffa08bad60>] ? insert_kthread_work+0x40/0x40
> >
> > Did you experiment with the snapshot chunk size (lvcreate --chunksize)?
> > I wonder if the default shapshot chunk size is the same on RHEL 7.4 and
> > Ubuntu you tried 4.14.39 on.
>
> I did not, but this shows 0:
>
> DR-[root@dmg-cbcache01 issdr]$ lvs -o+chunksize datavg/lvdb2
> LV VG Attr LSize Pool Origin Data% Meta% Move Log
> Cpy%Sync Convert Chunk
> lvdb2 datavg -wi-ao---- 70.00g
> 0
> lvdb2 datavg -wi-ao---- 70.00g
> 0
>
> root@lab2-b2:~# lvs -o+chunksize cerh1_cache_clone/data
> LV VG Attr LSize Pool Origin Data% Meta%
> Move Log Cpy%Sync Convert Chunk
> data cerh1_cache_clone -wi------- 90.00g
> 0
Chunk size is only relevant for snapshots, cache devices, etc.
Run that lvs command on a snapshot, like datavg/snap_data1.
Thanks,
Ilya
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