On 11.01.2018 05:03, Adam Borowski wrote:
> On Sun, Jan 07, 2018 at 01:17:19PM +0200, Nikolay Borisov wrote:
>> On  6.01.2018 07:10, Adam Borowski wrote:
>>> Hi!
>>> I got a reproducible infinite hang, reliably triggered by the testsuite of
>>> "flatpak"; fails on at least 4.15-rc6, 4.9.75, and on another machine with
>>> Debian's 4.14.2-1.
>>>
>>> [580632.355107] INFO: task kworker/u8:2:11105 blocked for more than 120 
>>> seconds.
>>> [580632.355120]       Not tainted 4.14.0-1-amd64 #1 Debian 4.14.2-1
>>> [580632.355124] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
>>> this message.
>>> [580632.355129] kworker/u8:2    D    0 11105      2 0x80000000
>>> [580632.355176] Workqueue: events_unbound 
>>> btrfs_async_reclaim_metadata_space [btrfs]
>>> [580632.355179] Call Trace:
>>> [580632.355192]  __schedule+0x28e/0x880
>>> [580632.355196]  schedule+0x2c/0x80
>>> [580632.355200]  wb_wait_for_completion+0x64/0x90
>>> [580632.355205]  ? finish_wait+0x80/0x80
>>> [580632.355207]  __writeback_inodes_sb_nr+0xa1/0xd0
>>> [580632.355210]  writeback_inodes_sb_nr+0x10/0x20
>>> [580632.355235]  flush_space+0x3ed/0x520 [btrfs]
>>> [580632.355238]  ? pick_next_task_fair+0x158/0x590
>>> [580632.355242]  ? __switch_to+0x1f3/0x460
>>> [580632.355267]  btrfs_async_reclaim_metadata_space+0xf6/0x4a0 [btrfs]
>>> [580632.355278]  process_one_work+0x198/0x390
>>> [580632.355281]  worker_thread+0x35/0x3c0
>>> [580632.355284]  kthread+0x125/0x140
>>> [580632.355287]  ? process_one_work+0x390/0x390
>>> [580632.355289]  ? kthread_create_on_node+0x70/0x70
>>> [580632.355292]  ? SyS_exit_group+0x14/0x20
>>> [580632.355295]  ret_from_fork+0x25/0x30

Frankly nothing in this stacktrace or any of the others you provided
suggest this is a problem in btrfs. If you look closely you'd see that
all the stacktraces are waiting on io completion in the generic
writeback layer. It seems the issue is writebacks never complete. What
makes you think this is a btrfs-specific problem?

>>>
>>> The machines are distinct enough that this probably should happen
>>> everywhere:
>>>
>>> AMD Phenom2, SSD, noatime,compress=lzo,space_cache=v2
>>> Intel Braswell, rust, noatime,autodefrag,space_cache=v2
> 
> It does cause data loss: while everything seems to work ok, files that are
> written to while there's this stuck worker become size 0 after rebooting.
> Only after a longish time other processes start getting stuck as well.
> 
> For this reason, I was reluctant to try on a real system -- but somehow I
> don't seem to be able to reproduce on minimal VMs.
> 
>> Provide output of echo w > /proc/sysrq-trigger when the hang happens.
> 
> [ 5679.403833] INFO: task kworker/u12:2:9904 blocked for more than 120 
> seconds.
> [ 5679.413938]       Not tainted 4.15.0-rc7-debug-00137-g13f8e1b5cc83 #1
> [ 5679.423336] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
> this message.
> [ 5679.434136] kworker/u12:2   D    0  9904      2 0x80000000
> [ 5679.442528] Workqueue: writeback wb_workfn (flush-btrfs-1)
> [ 5679.450809] Call Trace:
> [ 5679.455920]  ? __schedule+0x1a5/0x6e0
> [ 5679.462251]  ? check_preempt_curr+0x74/0x80
> [ 5679.468950]  ? atomic_t_wait+0x50/0x50
> [ 5679.475134]  schedule+0x23/0x80
> [ 5679.480670]  bit_wait+0x8/0x50
> [ 5679.485985]  __wait_on_bit+0x3d/0x80
> [ 5679.491828]  ? atomic_t_wait+0x50/0x50
> [ 5679.497726]  __inode_wait_for_writeback+0x9e/0xc0
> [ 5679.504531]  ? bit_waitqueue+0x30/0x30
> [ 5679.510292]  inode_wait_for_writeback+0x18/0x30
> [ 5679.516782]  evict+0xa4/0x180
> [ 5679.521596]  btrfs_run_delayed_iputs+0x61/0xb0
> [ 5679.527842]  btrfs_commit_transaction+0x7b0/0x8c0
> [ 5679.534310]  ? start_transaction+0xa0/0x390
> [ 5679.540151]  __writeback_single_inode+0x168/0x1b0
> [ 5679.546477]  writeback_sb_inodes+0x1be/0x420
> [ 5679.552264]  wb_writeback+0xe0/0x1d0
> [ 5679.557292]  wb_workfn+0x7d/0x2c0
> [ 5679.561984]  ? __switch_to+0x17c/0x370
> [ 5679.567045]  process_one_work+0x1a7/0x340
> [ 5679.572286]  worker_thread+0x26/0x3f0
> [ 5679.577043]  ? create_worker+0x190/0x190
> [ 5679.582007]  kthread+0x107/0x120
> [ 5679.586198]  ? kthread_create_worker_on_cpu+0x40/0x40
> [ 5679.592200]  ? kthread_create_worker_on_cpu+0x40/0x40
> [ 5679.598122]  ret_from_fork+0x1f/0x30
> [ 5679.602549] INFO: task testlibrary:12647 blocked for more than 120 seconds.
> [ 5679.610434]       Not tainted 4.15.0-rc7-debug-00137-g13f8e1b5cc83 #1
> [ 5679.617758] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
> this message.
> [ 5679.626453] testlibrary     D    0 12647  12606 0x00000000
> [ 5679.632812] Call Trace:
> [ 5679.636038]  ? __schedule+0x1a5/0x6e0
> [ 5679.640483]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5679.645881]  schedule+0x23/0x80
> [ 5679.649790]  wb_wait_for_completion+0x39/0x70
> [ 5679.654901]  ? wait_woken+0x80/0x80
> [ 5679.659092]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5679.664325]  sync_filesystem+0x21/0x80
> [ 5679.668797]  SyS_syncfs+0x44/0x90
> [ 5679.672809]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5679.678136] RIP: 0033:0x7fe82599e057
> [ 5679.682405] RSP: 002b:00007ffdfda6cf18 EFLAGS: 00000202
> [ 5679.682431] INFO: task pool:14436 blocked for more than 120 seconds.
> [ 5679.695395]       Not tainted 4.15.0-rc7-debug-00137-g13f8e1b5cc83 #1
> [ 5679.702499] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
> this message.
> [ 5679.711041] pool            D    0 14436      1 0x00000000
> [ 5679.717217] Call Trace:
> [ 5679.720280]  ? __schedule+0x1a5/0x6e0
> [ 5679.724619]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5679.729890]  schedule+0x23/0x80
> [ 5679.733698]  wb_wait_for_completion+0x39/0x70
> [ 5679.738748]  ? wait_woken+0x80/0x80
> [ 5679.742899]  sync_inodes_sb+0xb4/0x240
> [ 5679.747312]  sync_filesystem+0x4f/0x80
> [ 5679.751709]  SyS_syncfs+0x44/0x90
> [ 5679.755679]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5679.760935] RIP: 0033:0x7fb356793057
> [ 5679.765156] RSP: 002b:00007fb34f2c0128 EFLAGS: 00000202
> [ 5679.765173] INFO: task flatpak:14514 blocked for more than 120 seconds.
> [ 5679.778395]       Not tainted 4.15.0-rc7-debug-00137-g13f8e1b5cc83 #1
> [ 5679.785540] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
> this message.
> [ 5679.794171] flatpak         D    0 14514  12658 0x00000000
> [ 5679.800390] Call Trace:
> [ 5679.803440]  ? __schedule+0x1a5/0x6e0
> [ 5679.807735]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5679.813027]  schedule+0x23/0x80
> [ 5679.816805]  wb_wait_for_completion+0x39/0x70
> [ 5679.821809]  ? wait_woken+0x80/0x80
> [ 5679.825948]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5679.831133]  sync_filesystem+0x21/0x80
> [ 5679.835496]  SyS_syncfs+0x44/0x90
> [ 5679.839442]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5679.844744] RIP: 0033:0x7fe919246057
> [ 5679.848965] RSP: 002b:00007fff86bf7288 EFLAGS: 00000202
> [ 5679.848976] INFO: task flatpak:14728 blocked for more than 120 seconds.
> [ 5679.862238]       Not tainted 4.15.0-rc7-debug-00137-g13f8e1b5cc83 #1
> [ 5679.869360] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
> this message.
> [ 5679.877916] flatpak         D    0 14728  13226 0x00000000
> [ 5679.884129] Call Trace:
> [ 5679.887207]  ? __schedule+0x1a5/0x6e0
> [ 5679.891562]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5679.896882]  schedule+0x23/0x80
> [ 5679.900709]  wb_wait_for_completion+0x39/0x70
> [ 5679.905749]  ? wait_woken+0x80/0x80
> [ 5679.909916]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5679.915162]  sync_filesystem+0x21/0x80
> [ 5679.919603]  SyS_syncfs+0x44/0x90
> [ 5679.923599]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5679.928902] RIP: 0033:0x7fae19413057
> [ 5679.933150] RSP: 002b:00007ffd3e6bfea8 EFLAGS: 00000246
> [ 5679.933164] INFO: task flatpak:14948 blocked for more than 120 seconds.
> [ 5679.946442]       Not tainted 4.15.0-rc7-debug-00137-g13f8e1b5cc83 #1
> [ 5679.953577] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
> this message.
> [ 5679.962110] flatpak         D    0 14948  12759 0x00000000
> [ 5679.968382] Call Trace:
> [ 5679.971453]  ? __schedule+0x1a5/0x6e0
> [ 5679.975801]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5679.981134]  schedule+0x23/0x80
> [ 5679.984933]  wb_wait_for_completion+0x39/0x70
> [ 5679.989965]  ? wait_woken+0x80/0x80
> [ 5679.994163]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5679.999365]  sync_filesystem+0x21/0x80
> [ 5680.003819]  SyS_syncfs+0x44/0x90
> [ 5680.007781]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5680.013160] RIP: 0033:0x7f478310e057
> [ 5680.017421] RSP: 002b:00007ffd73a67218 EFLAGS: 00000246
> [ 5680.017433] INFO: task flatpak:15011 blocked for more than 120 seconds.
> [ 5680.030701]       Not tainted 4.15.0-rc7-debug-00137-g13f8e1b5cc83 #1
> [ 5680.037822] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables 
> this message.
> [ 5680.046373] flatpak         D    0 15011  12798 0x00000000
> [ 5680.052602] Call Trace:
> [ 5680.055682]  ? __schedule+0x1a5/0x6e0
> [ 5680.060058]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5680.065417]  schedule+0x23/0x80
> [ 5680.069204]  wb_wait_for_completion+0x39/0x70
> [ 5680.074290]  ? wait_woken+0x80/0x80
> [ 5680.078442]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5680.083677]  sync_filesystem+0x21/0x80
> [ 5680.088091]  SyS_syncfs+0x44/0x90
> [ 5680.092085]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5680.097418] RIP: 0033:0x7f0b36769057
> [ 5680.101699] RSP: 002b:00007ffc0da951f8 EFLAGS: 00000246
> 
> [ 5693.149233] sysrq: SysRq : Show Blocked State
> [ 5693.167203]   task                        PC stack   pid father
> [ 5693.177433] kworker/u12:2   D    0  9904      2 0x80000000
> [ 5693.187073] Workqueue: writeback wb_workfn (flush-btrfs-1)
> [ 5693.196725] Call Trace:
> [ 5693.203260]  ? __schedule+0x1a5/0x6e0
> [ 5693.211069]  ? check_preempt_curr+0x74/0x80
> [ 5693.219360]  ? atomic_t_wait+0x50/0x50
> [ 5693.227185]  schedule+0x23/0x80
> [ 5693.234390]  bit_wait+0x8/0x50
> [ 5693.241482]  __wait_on_bit+0x3d/0x80
> [ 5693.249104]  ? atomic_t_wait+0x50/0x50
> [ 5693.256882]  __inode_wait_for_writeback+0x9e/0xc0
> [ 5693.265687]  ? bit_waitqueue+0x30/0x30
> [ 5693.273489]  inode_wait_for_writeback+0x18/0x30
> [ 5693.282092]  evict+0xa4/0x180
> [ 5693.289042]  btrfs_run_delayed_iputs+0x61/0xb0
> [ 5693.297478]  btrfs_commit_transaction+0x7b0/0x8c0
> [ 5693.306156]  ? start_transaction+0xa0/0x390
> [ 5693.314215]  __writeback_single_inode+0x168/0x1b0
> [ 5693.322824]  writeback_sb_inodes+0x1be/0x420
> [ 5693.331013]  wb_writeback+0xe0/0x1d0
> [ 5693.338452]  wb_workfn+0x7d/0x2c0
> [ 5693.345622]  ? __switch_to+0x17c/0x370
> [ 5693.353252]  process_one_work+0x1a7/0x340
> [ 5693.361138]  worker_thread+0x26/0x3f0
> [ 5693.368673]  ? create_worker+0x190/0x190
> [ 5693.376459]  kthread+0x107/0x120
> [ 5693.383532]  ? kthread_create_worker_on_cpu+0x40/0x40
> [ 5693.392494]  ? kthread_create_worker_on_cpu+0x40/0x40
> [ 5693.401390]  ret_from_fork+0x1f/0x30
> [ 5693.408823] testlibrary     D    0 12647  12606 0x00000000
> [ 5693.418201] Call Trace:
> [ 5693.424392]  ? __schedule+0x1a5/0x6e0
> [ 5693.431751]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5693.440035]  schedule+0x23/0x80
> [ 5693.446831]  wb_wait_for_completion+0x39/0x70
> [ 5693.454857]  ? wait_woken+0x80/0x80
> [ 5693.462002]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5693.470229]  sync_filesystem+0x21/0x80
> [ 5693.477625]  SyS_syncfs+0x44/0x90
> [ 5693.484547]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5693.492823] RIP: 0033:0x7fe82599e057
> [ 5693.500018] RSP: 002b:00007ffdfda6cf18 EFLAGS: 00000202
> [ 5693.500050] pool            D    0 14436      1 0x00000000
> [ 5693.518253] Call Trace:
> [ 5693.524294]  ? __schedule+0x1a5/0x6e0
> [ 5693.531590]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5693.539833]  schedule+0x23/0x80
> [ 5693.546564]  wb_wait_for_completion+0x39/0x70
> [ 5693.554496]  ? wait_woken+0x80/0x80
> [ 5693.561468]  sync_inodes_sb+0xb4/0x240
> [ 5693.568678]  sync_filesystem+0x4f/0x80
> [ 5693.575860]  SyS_syncfs+0x44/0x90
> [ 5693.582610]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5693.590716] RIP: 0033:0x7fb356793057
> [ 5693.597716] RSP: 002b:00007fb34f2c0128 EFLAGS: 00000202
> [ 5693.597721] flatpak         D    0 14514  12658 0x00000000
> [ 5693.615475] Call Trace:
> [ 5693.621387]  ? __schedule+0x1a5/0x6e0
> [ 5693.628482]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5693.636552]  schedule+0x23/0x80
> [ 5693.643158]  wb_wait_for_completion+0x39/0x70
> [ 5693.650979]  ? wait_woken+0x80/0x80
> [ 5693.657928]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5693.665904]  sync_filesystem+0x21/0x80
> [ 5693.673110]  SyS_syncfs+0x44/0x90
> [ 5693.679802]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5693.687858] RIP: 0033:0x7fe919246057
> [ 5693.694820] RSP: 002b:00007fff86bf7288 EFLAGS: 00000202
> [ 5693.694827] flatpak         D    0 14728  13226 0x00000000
> [ 5693.712525] Call Trace:
> [ 5693.718340]  ? __schedule+0x1a5/0x6e0
> [ 5693.725433]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5693.733536]  schedule+0x23/0x80
> [ 5693.740143]  wb_wait_for_completion+0x39/0x70
> [ 5693.747989]  ? wait_woken+0x80/0x80
> [ 5693.754947]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5693.762977]  sync_filesystem+0x21/0x80
> [ 5693.770224]  SyS_syncfs+0x44/0x90
> [ 5693.777002]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5693.785128] RIP: 0033:0x7fae19413057
> [ 5693.792160] RSP: 002b:00007ffd3e6bfea8 EFLAGS: 00000246
> [ 5693.792167] flatpak         D    0 14948  12759 0x00000000
> [ 5693.809982] Call Trace:
> [ 5693.815894]  ? __schedule+0x1a5/0x6e0
> [ 5693.823054]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5693.831225]  schedule+0x23/0x80
> [ 5693.837851]  wb_wait_for_completion+0x39/0x70
> [ 5693.845736]  ? wait_woken+0x80/0x80
> [ 5693.852727]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5693.860862]  sync_filesystem+0x21/0x80
> [ 5693.868132]  SyS_syncfs+0x44/0x90
> [ 5693.875017]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5693.883237] RIP: 0033:0x7f478310e057
> [ 5693.890352] RSP: 002b:00007ffd73a67218 EFLAGS: 00000246
> [ 5693.890357] flatpak         D    0 15011  12798 0x00000000
> [ 5693.908228] Call Trace:
> [ 5693.914196]  ? __schedule+0x1a5/0x6e0
> [ 5693.921402]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5693.929611]  schedule+0x23/0x80
> [ 5693.936316]  wb_wait_for_completion+0x39/0x70
> [ 5693.944271]  ? wait_woken+0x80/0x80
> [ 5693.951303]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5693.959447]  sync_filesystem+0x21/0x80
> [ 5693.966778]  SyS_syncfs+0x44/0x90
> [ 5693.973654]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5693.981816] RIP: 0033:0x7f0b36769057
> [ 5693.988935] RSP: 002b:00007ffc0da951f8 EFLAGS: 00000246
> 
> [ 5702.930722] sysrq: SysRq : Show Blocked State
> [ 5702.947430]   task                        PC stack   pid father
> [ 5702.957101] kworker/u12:2   D    0  9904      2 0x80000000
> [ 5702.966186] Workqueue: writeback wb_workfn (flush-btrfs-1)
> [ 5702.975298] Call Trace:
> [ 5702.981336]  ? __schedule+0x1a5/0x6e0
> [ 5702.988605]  ? check_preempt_curr+0x74/0x80
> [ 5702.996390]  ? atomic_t_wait+0x50/0x50
> [ 5703.003764]  schedule+0x23/0x80
> [ 5703.010507]  bit_wait+0x8/0x50
> [ 5703.017144]  __wait_on_bit+0x3d/0x80
> [ 5703.024270]  ? atomic_t_wait+0x50/0x50
> [ 5703.031558]  __inode_wait_for_writeback+0x9e/0xc0
> [ 5703.039822]  ? bit_waitqueue+0x30/0x30
> [ 5703.047116]  inode_wait_for_writeback+0x18/0x30
> [ 5703.055205]  evict+0xa4/0x180
> [ 5703.061698]  btrfs_run_delayed_iputs+0x61/0xb0
> [ 5703.069695]  btrfs_commit_transaction+0x7b0/0x8c0
> [ 5703.077970]  ? start_transaction+0xa0/0x390
> [ 5703.085721]  __writeback_single_inode+0x168/0x1b0
> [ 5703.093990]  writeback_sb_inodes+0x1be/0x420
> [ 5703.101817]  wb_writeback+0xe0/0x1d0
> [ 5703.108935]  wb_workfn+0x7d/0x2c0
> [ 5703.115764]  ? __switch_to+0x17c/0x370
> [ 5703.123043]  process_one_work+0x1a7/0x340
> [ 5703.130546]  worker_thread+0x26/0x3f0
> [ 5703.137710]  ? create_worker+0x190/0x190
> [ 5703.145127]  kthread+0x107/0x120
> [ 5703.151813]  ? kthread_create_worker_on_cpu+0x40/0x40
> [ 5703.160362]  ? kthread_create_worker_on_cpu+0x40/0x40
> [ 5703.168870]  ret_from_fork+0x1f/0x30
> [ 5703.175948] testlibrary     D    0 12647  12606 0x00000000
> [ 5703.184926] Call Trace:
> [ 5703.190824]  ? __schedule+0x1a5/0x6e0
> [ 5703.197950]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5703.206098]  schedule+0x23/0x80
> [ 5703.212732]  wb_wait_for_completion+0x39/0x70
> [ 5703.220581]  ? wait_woken+0x80/0x80
> [ 5703.227549]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5703.235558]  sync_filesystem+0x21/0x80
> [ 5703.242793]  SyS_syncfs+0x44/0x90
> [ 5703.249570]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5703.257666] RIP: 0033:0x7fe82599e057
> [ 5703.264707] RSP: 002b:00007ffdfda6cf18 EFLAGS: 00000202
> [ 5703.264736] pool            D    0 14436      1 0x00000000
> [ 5703.282426] Call Trace:
> [ 5703.288348]  ? __schedule+0x1a5/0x6e0
> [ 5703.295511]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5703.303593]  schedule+0x23/0x80
> [ 5703.310201]  wb_wait_for_completion+0x39/0x70
> [ 5703.318023]  ? wait_woken+0x80/0x80
> [ 5703.325008]  sync_inodes_sb+0xb4/0x240
> [ 5703.332208]  sync_filesystem+0x4f/0x80
> [ 5703.339370]  SyS_syncfs+0x44/0x90
> [ 5703.346100]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5703.354128] RIP: 0033:0x7fb356793057
> [ 5703.361128] RSP: 002b:00007fb34f2c0128 EFLAGS: 00000202
> [ 5703.361134] flatpak         D    0 14514  12658 0x00000000
> [ 5703.378754] Call Trace:
> [ 5703.384622]  ? __schedule+0x1a5/0x6e0
> [ 5703.391709]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5703.399780]  schedule+0x23/0x80
> [ 5703.406359]  wb_wait_for_completion+0x39/0x70
> [ 5703.414158]  ? wait_woken+0x80/0x80
> [ 5703.421041]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5703.428961]  sync_filesystem+0x21/0x80
> [ 5703.436118]  SyS_syncfs+0x44/0x90
> [ 5703.442782]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5703.450734] RIP: 0033:0x7fe919246057
> [ 5703.457664] RSP: 002b:00007fff86bf7288 EFLAGS: 00000202
> [ 5703.457670] flatpak         D    0 14728  13226 0x00000000
> [ 5703.475169] Call Trace:
> [ 5703.480987]  ? __schedule+0x1a5/0x6e0
> [ 5703.488057]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5703.496106]  schedule+0x23/0x80
> [ 5703.502667]  wb_wait_for_completion+0x39/0x70
> [ 5703.510447]  ? wait_woken+0x80/0x80
> [ 5703.517345]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5703.525294]  sync_filesystem+0x21/0x80
> [ 5703.532447]  SyS_syncfs+0x44/0x90
> [ 5703.539161]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5703.547197] RIP: 0033:0x7fae19413057
> [ 5703.554192] RSP: 002b:00007ffd3e6bfea8 EFLAGS: 00000246
> [ 5703.554199] flatpak         D    0 14948  12759 0x00000000
> [ 5703.571833] Call Trace:
> [ 5703.577715]  ? __schedule+0x1a5/0x6e0
> [ 5703.584815]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5703.592924]  schedule+0x23/0x80
> [ 5703.599505]  wb_wait_for_completion+0x39/0x70
> [ 5703.607337]  ? wait_woken+0x80/0x80
> [ 5703.614278]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5703.622321]  sync_filesystem+0x21/0x80
> [ 5703.629544]  SyS_syncfs+0x44/0x90
> [ 5703.636346]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5703.644461] RIP: 0033:0x7f478310e057
> [ 5703.651515] RSP: 002b:00007ffd73a67218 EFLAGS: 00000246
> [ 5703.651520] flatpak         D    0 15011  12798 0x00000000
> [ 5703.669280] Call Trace:
> [ 5703.675215]  ? __schedule+0x1a5/0x6e0
> [ 5703.682367]  ? bdi_split_work_to_wbs+0x159/0x290
> [ 5703.690521]  schedule+0x23/0x80
> [ 5703.697150]  wb_wait_for_completion+0x39/0x70
> [ 5703.705026]  ? wait_woken+0x80/0x80
> [ 5703.712000]  __writeback_inodes_sb_nr+0x95/0xa0
> [ 5703.720071]  sync_filesystem+0x21/0x80
> [ 5703.727336]  SyS_syncfs+0x44/0x90
> [ 5703.734134]  entry_SYSCALL_64_fastpath+0x17/0x70
> [ 5703.742254] RIP: 0033:0x7f0b36769057
> [ 5703.749328] RSP: 002b:00007ffc0da951f8 EFLAGS: 00000246
> 
> [ 5711.188611] sysrq: SysRq : Resetting
> 
> 
> Meow!
> 
--
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