Re: btrfs induced data loss (on xfs) - 5.19.0-38-generic

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2023/4/17 13:20, Kyle Sanderson wrote:
> The single btrfs disk was at 100% utilization and a wa of 50~, reading
> back at around 2MB/s. df and similar would simply freeze. Leading up
> to this I removed around 2T of data from a single btrfs disk. I
> managed to get most of the services shutdown and disks unmounted, but
> when the system came back up I had to use xfs_repair (for the first
> time in a very long time) to boot into my system. I likely should have
> just pulled the power...

I didn't see any obvious btrfs related work involved in the call trace.
Thus I believe it's not really hanging in a waiting status.

And talking about the "100% utilization", did you mean a single CPU core 
is fully utilized by some btrfs thread?

If so, it looks like qgroup is involved.
Did you just recently deleted one or more snapshots? If so, it's almost 
certain qgroup is the cause of the 100% CPU utilization.

In that case, you can disable quota for that btrfs (permanently), or use 
newer kernel which has a sysfs interface:

   /sys/fs/btrfs/<UUID>/qgroups/drop_subtree_threshold

If you write some value like 3 into that file, btrfs would automatically 
avoid such long CPU usage caused by large snapshot dropping.

But talking about the XFS corruption, I'm not sure how btrfs can lead to 
problems in XFS...

Thanks,
Qu
> 
> [1147997.255020] INFO: task happywriter:3425205 blocked for more than
> 120 seconds.
> [1147997.255088]       Not tainted 5.19.0-38-generic #39~22.04.1-Ubuntu
> [1147997.255114] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [1147997.255144] task:happywriter state:D stack:    0 pid:3425205
> ppid:557021 flags:0x00004000
> [1147997.255151] Call Trace:
> [1147997.255155]  <TASK>
> [1147997.255160]  __schedule+0x257/0x5d0
> [1147997.255169]  ? __schedule+0x25f/0x5d0
> [1147997.255173]  schedule+0x68/0x110
> [1147997.255176]  rwsem_down_write_slowpath+0x2ee/0x5a0
> [1147997.255180]  ? check_heap_object+0x100/0x1e0
> [1147997.255185]  down_write+0x4f/0x70
> [1147997.255189]  do_unlinkat+0x12b/0x2d0
> [1147997.255194]  __x64_sys_unlink+0x42/0x70
> [1147997.255197]  ? syscall_exit_to_user_mode+0x2a/0x50
> [1147997.255201]  do_syscall_64+0x59/0x90
> [1147997.255204]  ? do_syscall_64+0x69/0x90
> [1147997.255207]  ? sysvec_call_function_single+0x4e/0xb0
> [1147997.255211]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [1147997.255216] RIP: 0033:0x1202a57
> [1147997.255220] RSP: 002b:00007fe467ffd4c8 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000057
> [1147997.255224] RAX: ffffffffffffffda RBX: 00007fe3a4e94d28 RCX:
> 0000000001202a57
> [1147997.255226] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> 00007fe450054b60
> [1147997.255228] RBP: 00007fe450054b60 R08: 0000000000000000 R09:
> 00000000000000e8
> [1147997.255231] R10: 0000000000000001 R11: 0000000000000246 R12:
> 00007fe467ffd5b0
> [1147997.255233] R13: 00007fe467ffd5f0 R14: 00007fe467ffd5e0 R15:
> 00007fe3a4e94d28
> [1147997.255239]  </TASK>
> [1148118.087966] INFO: task happywriter:3425205 blocked for more than
> 241 seconds.
> [1148118.088022]       Not tainted 5.19.0-38-generic #39~22.04.1-Ubuntu
> [1148118.088048] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [1148118.088077] task:happywriter state:D stack:    0 pid:3425205
> ppid:557021 flags:0x00004000
> [1148118.088083] Call Trace:
> [1148118.088087]  <TASK>
> [1148118.088093]  __schedule+0x257/0x5d0
> [1148118.088101]  ? __schedule+0x25f/0x5d0
> [1148118.088105]  schedule+0x68/0x110
> [1148118.088108]  rwsem_down_write_slowpath+0x2ee/0x5a0
> [1148118.088113]  ? check_heap_object+0x100/0x1e0
> [1148118.088118]  down_write+0x4f/0x70
> [1148118.088121]  do_unlinkat+0x12b/0x2d0
> [1148118.088126]  __x64_sys_unlink+0x42/0x70
> [1148118.088129]  ? syscall_exit_to_user_mode+0x2a/0x50
> [1148118.088133]  do_syscall_64+0x59/0x90
> [1148118.088136]  ? do_syscall_64+0x69/0x90
> [1148118.088139]  ? sysvec_call_function_single+0x4e/0xb0
> [1148118.088142]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [1148118.088148] RIP: 0033:0x1202a57
> [1148118.088151] RSP: 002b:00007fe467ffd4c8 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000057
> [1148118.088155] RAX: ffffffffffffffda RBX: 00007fe3a4e94d28 RCX:
> 0000000001202a57
> [1148118.088158] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> 00007fe450054b60
> [1148118.088160] RBP: 00007fe450054b60 R08: 0000000000000000 R09:
> 00000000000000e8
> [1148118.088162] R10: 0000000000000001 R11: 0000000000000246 R12:
> 00007fe467ffd5b0
> [1148118.088164] R13: 00007fe467ffd5f0 R14: 00007fe467ffd5e0 R15:
> 00007fe3a4e94d28
> [1148118.088170]  </TASK>
> [1148238.912688] INFO: task kcompactd0:70 blocked for more than 120 seconds.
> [1148238.912741]       Not tainted 5.19.0-38-generic #39~22.04.1-Ubuntu
> [1148238.912767] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [1148238.912796] task:kcompactd0      state:D stack:    0 pid:   70
> ppid:     2 flags:0x00004000
> [1148238.912803] Call Trace:
> [1148238.912806]  <TASK>
> [1148238.912812]  __schedule+0x257/0x5d0
> [1148238.912821]  schedule+0x68/0x110
> [1148238.912824]  io_schedule+0x46/0x80
> [1148238.912827]  folio_wait_bit_common+0x14c/0x3a0
> [1148238.912833]  ? filemap_invalidate_unlock_two+0x50/0x50
> [1148238.912838]  __folio_lock+0x17/0x30
> [1148238.912842]  __unmap_and_move.constprop.0+0x39c/0x640
> [1148238.912847]  ? free_unref_page+0xe3/0x190
> [1148238.912852]  ? move_freelist_tail+0xe0/0xe0
> [1148238.912855]  ? move_freelist_tail+0xe0/0xe0
> [1148238.912858]  unmap_and_move+0x7d/0x4e0
> [1148238.912862]  migrate_pages+0x3b8/0x770
> [1148238.912867]  ? move_freelist_tail+0xe0/0xe0
> [1148238.912870]  ? isolate_freepages+0x2f0/0x2f0
> [1148238.912874]  compact_zone+0x2ca/0x620
> [1148238.912878]  proactive_compact_node+0x8a/0xe0
> [1148238.912883]  kcompactd+0x21c/0x4e0
> [1148238.912886]  ? destroy_sched_domains_rcu+0x40/0x40
> [1148238.912892]  ? kcompactd_do_work+0x240/0x240
> [1148238.912896]  kthread+0xeb/0x120
> [1148238.912900]  ? kthread_complete_and_exit+0x20/0x20
> [1148238.912904]  ret_from_fork+0x1f/0x30
> [1148238.912911]  </TASK>
> [1148238.913163] INFO: task happywriter:3425205 blocked for more than
> 362 seconds.
> [1148238.913195]       Not tainted 5.19.0-38-generic #39~22.04.1-Ubuntu
> [1148238.913220] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [1148238.913250] task:happywriter state:D stack:    0 pid:3425205
> ppid:557021 flags:0x00004000
> [1148238.913254] Call Trace:
> [1148238.913256]  <TASK>
> [1148238.913259]  __schedule+0x257/0x5d0
> [1148238.913264]  ? __schedule+0x25f/0x5d0
> [1148238.913267]  schedule+0x68/0x110
> [1148238.913270]  rwsem_down_write_slowpath+0x2ee/0x5a0
> [1148238.913276]  ? check_heap_object+0x100/0x1e0
> [1148238.913280]  down_write+0x4f/0x70
> [1148238.913284]  do_unlinkat+0x12b/0x2d0
> [1148238.913288]  __x64_sys_unlink+0x42/0x70
> [1148238.913292]  ? syscall_exit_to_user_mode+0x2a/0x50
> [1148238.913296]  do_syscall_64+0x59/0x90
> [1148238.913299]  ? do_syscall_64+0x69/0x90
> [1148238.913301]  ? sysvec_call_function_single+0x4e/0xb0
> [1148238.913305]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [1148238.913310] RIP: 0033:0x1202a57
> [1148238.913315] RSP: 002b:00007fe467ffd4c8 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000057
> [1148238.913319] RAX: ffffffffffffffda RBX: 00007fe3a4e94d28 RCX:
> 0000000001202a57
> [1148238.913321] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> 00007fe450054b60
> [1148238.913323] RBP: 00007fe450054b60 R08: 0000000000000000 R09:
> 00000000000000e8
> [1148238.913325] R10: 0000000000000001 R11: 0000000000000246 R12:
> 00007fe467ffd5b0
> [1148238.913328] R13: 00007fe467ffd5f0 R14: 00007fe467ffd5e0 R15:
> 00007fe3a4e94d28
> [1148238.913333]  </TASK>
> [1148238.913429] INFO: task kworker/u16:20:3402199 blocked for more
> than 120 seconds.
> [1148238.913459]       Not tainted 5.19.0-38-generic #39~22.04.1-Ubuntu
> [1148238.913496] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [1148238.913527] task:kworker/u16:20  state:D stack:    0 pid:3402199
> ppid:     2 flags:0x00004000
> [1148238.913533] Workqueue: events_unbound io_ring_exit_work
> [1148238.913539] Call Trace:
> [1148238.913541]  <TASK>
> [1148238.913544]  __schedule+0x257/0x5d0
> [1148238.913548]  schedule+0x68/0x110
> [1148238.913551]  schedule_timeout+0x122/0x160
> [1148238.913556]  __wait_for_common+0x8f/0x190
> [1148238.913559]  ? usleep_range_state+0xa0/0xa0
> [1148238.913564]  wait_for_completion+0x24/0x40
> [1148238.913567]  io_ring_exit_work+0x186/0x1e9
> [1148238.913571]  ? io_uring_del_tctx_node+0xbf/0xbf
> [1148238.913576]  process_one_work+0x21c/0x400
> [1148238.913579]  worker_thread+0x50/0x3f0
> [1148238.913583]  ? rescuer_thread+0x3a0/0x3a0
> [1148238.913586]  kthread+0xeb/0x120
> [1148238.913590]  ? kthread_complete_and_exit+0x20/0x20
> [1148238.913594]  ret_from_fork+0x1f/0x30
> [1148238.913600]  </TASK>
> [1148238.913607] INFO: task stat:3434604 blocked for more than 120 seconds.
> [1148238.913633]       Not tainted 5.19.0-38-generic #39~22.04.1-Ubuntu
> [1148238.913658] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [1148238.913687] task:stat            state:D stack:    0 pid:3434604
> ppid:3396625 flags:0x00004004
> [1148238.913691] Call Trace:
> [1148238.913693]  <TASK>
> [1148238.913695]  __schedule+0x257/0x5d0
> [1148238.913699]  schedule+0x68/0x110
> [1148238.913703]  request_wait_answer+0x13f/0x220
> [1148238.913708]  ? destroy_sched_domains_rcu+0x40/0x40
> [1148238.913713]  fuse_simple_request+0x1bb/0x370
> [1148238.913717]  fuse_do_getattr+0xda/0x320
> [1148238.913720]  ? try_to_unlazy+0x5b/0xd0
> [1148238.913726]  fuse_update_get_attr+0xb3/0xf0
> [1148238.913730]  fuse_getattr+0x87/0xd0
> [1148238.913733]  vfs_getattr_nosec+0xba/0x100
> [1148238.913737]  vfs_statx+0xa9/0x140
> [1148238.913741]  vfs_fstatat+0x59/0x80
> [1148238.913744]  __do_sys_newlstat+0x38/0x80
> [1148238.913750]  __x64_sys_newlstat+0x16/0x20
> [1148238.913753]  do_syscall_64+0x59/0x90
> [1148238.913757]  ? handle_mm_fault+0xba/0x2a0
> [1148238.913761]  ? exit_to_user_mode_prepare+0xaf/0xd0
> [1148238.913765]  ? irqentry_exit_to_user_mode+0x9/0x20
> [1148238.913769]  ? irqentry_exit+0x43/0x50
> [1148238.913772]  ? exc_page_fault+0x92/0x1b0
> [1148238.913776]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [1148238.913780] RIP: 0033:0x7fa76960d6ea
> [1148238.913783] RSP: 002b:00007ffe6d011878 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000006
> [1148238.913787] RAX: ffffffffffffffda RBX: 0000000000000001 RCX:
> 00007fa76960d6ea
> [1148238.913789] RDX: 00007ffe6d011890 RSI: 00007ffe6d011890 RDI:
> 00007ffe6d01290b
> [1148238.913791] RBP: 00007ffe6d011a70 R08: 0000000000000001 R09:
> 0000000000000000
> [1148238.913793] R10: fffffffffffff3ce R11: 0000000000000246 R12:
> 0000000000000000
> [1148238.913795] R13: 000055feff0d2960 R14: 00007ffe6d011a68 R15:
> 00007ffe6d01290b
> [1148238.913800]  </TASK>