Dne 01. 08. 22 v 19:29 Zdenek Kabelac napsal(a):
Dne 30. 07. 22 v 18:33 Thomas Deutschmann napsal(a):
Hi,
while trying to backup a Dell R7525 system running
Debian bookworm/testing using LVM snapshots I noticed that the system
will 'freeze' sometimes (not all the times) when creating the snapshot.
To recover from this, a power cycle is required.
Is this a problem caused by LVM or a kernel issue?
The command I run:
/usr/sbin/lvcreate \
-vvvvv \
--size 100G \
--snapshot /dev/mapper/devDataStore1-volMachines \
--name volMachines_snap
The last 4 lines:
[Sat Jul 30 16:31:34 2022] debugfs: Directory 'dm-4' with parent 'block'
already present!
[Sat Jul 30 16:31:34 2022] debugfs: Directory 'dm-7' with parent 'block'
already present!
[Sat Jul 30 16:34:55 2022] INFO: task mariadbd:1607 blocked for more than
120 seconds.
[Sat Jul 30 16:34:55 2022] Not tainted 5.18.0-2-amd64 #1 Debian 5.18.5-1
[Sat Jul 30 16:34:55 2022] "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
[Sat Jul 30 16:34:55 2022] task:mariadbd state:D stack: 0 pid:
1607 ppid: 1289 flags:0x00000000
[Sat Jul 30 16:34:55 2022] Call Trace:
[Sat Jul 30 16:34:55 2022] <TASK>
[Sat Jul 30 16:34:55 2022] __schedule+0x30b/0x9e0
[Sat Jul 30 16:34:55 2022] schedule+0x4e/0xb0
[Sat Jul 30 16:34:55 2022] percpu_rwsem_wait+0x112/0x130
[Sat Jul 30 16:34:55 2022] ? __percpu_rwsem_trylock.part.0+0x70/0x70
[Sat Jul 30 16:34:55 2022] __percpu_down_read+0x5e/0x80
[Sat Jul 30 16:34:55 2022] io_write+0x2e9/0x300
[Sat Jul 30 16:34:55 2022] ? _raw_spin_lock+0x13/0x30
[Sat Jul 30 16:34:55 2022] ? newidle_balance+0x26a/0x400
[Sat Jul 30 16:34:55 2022] ? fget+0x7c/0xb0
[Sat Jul 30 16:34:55 2022] io_issue_sqe+0x47c/0x2550
[Sat Jul 30 16:34:55 2022] ? select_task_rq_fair+0x174/0x1240
[Sat Jul 30 16:34:55 2022] ? hrtimer_try_to_cancel+0x78/0x110
[Sat Jul 30 16:34:55 2022] io_submit_sqes+0x3ce/0x1aa0
[Sat Jul 30 16:34:55 2022] ? _raw_spin_unlock_irqrestore+0x23/0x40
[Sat Jul 30 16:34:55 2022] ? wake_up_q+0x4a/0x90
[Sat Jul 30 16:34:55 2022] ? __do_sys_io_uring_enter+0x565/0xa60
[Sat Jul 30 16:34:55 2022] __do_sys_io_uring_enter+0x565/0xa60
[Sat Jul 30 16:34:55 2022] do_syscall_64+0x3b/0xc0
[Sat Jul 30 16:34:55 2022] entry_SYSCALL_64_after_hwframe+0x44/0xae
[Sat Jul 30 16:34:55 2022] RIP: 0033:0x7f05b90229b9
[Sat Jul 30 16:34:55 2022] RSP: 002b:00007eff8e9efa38 EFLAGS: 00000216
ORIG_RAX: 00000000000001aa
[Sat Jul 30 16:34:55 2022] RAX: ffffffffffffffda RBX: 0000561c424f1d18 RCX:
00007f05b90229b9
[Sat Jul 30 16:34:55 2022] RDX: 0000000000000000 RSI: 0000000000000001 RDI:
0000000000000009
[Sat Jul 30 16:34:55 2022] RBP: 00007eff8e9efa90 R08: 0000000000000000 R09:
0000000000000008
[Sat Jul 30 16:34:55 2022] R10: 0000000000000000 R11: 0000000000000216 R12:
0000561c42500938
[Sat Jul 30 16:34:55 2022] R13: 00007f05b9821c00 R14: 0000561c425009e0 R15:
0000561c424f1d18
[Sat Jul 30 16:34:55 2022] </TASK>
[Sat Jul 30 16:34:55 2022] INFO: task mariadbd:9955 blocked for more than
120 seconds.
[Sat Jul 30 16:34:55 2022] Not tainted 5.18.0-2-amd64 #1 Debian 5.18.5-1
[Sat Jul 30 16:34:55 2022] "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
[Sat Jul 30 16:34:55 2022] task:mariadbd state:D stack: 0 pid:
9955 ppid: 1289 flags:0x00000000
[Sat Jul 30 16:34:55 2022] Call Trace:
[Sat Jul 30 16:34:55 2022] <TASK>
[...]
The message "mariadbd:1607 blocked for more than 120 seconds" will repeat.
MariaDB itself is running in a systemd-nspawn container. The container
storage is located on the volume for which snapshot creation will hang.
Hi
Lvm2 is *NOT* supported to be used within containers!
This requires some very specific 'system' modification and its in overal very
problematic - so rule #1 is - always run lvm2 command on your hosting machine.
Now - you suggests you are able to reproduce this issue also on your bare
metal hw - in this case run these 3 commands before 'lvcreate'
# dmsetup table
# dmsetup info -c
# dmsetup ls --tree
# lvcreate ....
If it blocks take again these:
# dmsetup table
# dmsetup info -c
# dmsetup ls --tree
You 'lvcreate -vvvv' & 'dmesg' trace simply suggest that system is waiting to
fulfill 'fsfreeze' operation - it's unclear why it cannot be finished -
maybe some problem with your 'raid' array ??
So far I do not see any bug on lvm2 side - all works from lvm2 side as
expected - however it's unclear why your 'raid' is so slow ?
Note: you could always 'experiment' without lvm2 in the picture -
you can ran 'fsfreeze --freeze|--unfreeze' yourself - to see whether even
this command is able to finish ?
Note2: if you system has lots of 'dirty' pages - it may potentially take a lot
of time to 'fsfreeze' operation of a filesystem since all 'dirty' pages needs
to be written to your disk..
Forgot to mention typical problem with container is a 'missing udevd' -
resulting endless waiting on 'cookie' confirmation on lvm2 side.
This could be usually 'resolved' by issueing:
'dmsetup udevcomplete_all'
(you could see 'dmsetup udevcookies' in-flight operations)
But that should not be a problem if you are waiting on 'fsfreeze'....
Regards
Zdenek
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