[12398]     0 12398    18112     8736      24       3        0          1000 syz-executor.3
[12400]     0 12400    18145     8738      24       3        0          1000 syz-executor.3
[12421]     0 12421    18112     8736      24       3        0          1000 syz-executor.3
[12422]     0 12422    18145     8738      24       3        0          1000 syz-executor.3
[12425]     0 12425    18112     8736      24       3        0          1000 syz-executor.3
INFO: task kworker/0:0:4 blocked for more than 140 seconds.
      Not tainted 4.9.141+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/0:0     D27640     4      2 0x80000000
Workqueue: events proc_cleanup_work
 ffff8801da5fc740 ffff8801982d8580 ffff88019b9d1080 ffff8801a62f4740
 ffff8801db621018 ffff8801da6677f0 ffffffff828075c2 ffffffff83c4bfe8
 0000000041b58ab3 ffffffff82e33920 00ffffff83c7a7d0 ffff8801db6218f0
Call Trace:
 [<ffffffff82808aef>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff828142d5>] schedule_timeout+0x735/0xe20 kernel/time/timer.c:1771
 [<ffffffff8280a63f>] do_wait_for_common kernel/sched/completion.c:75 [inline]
 [<ffffffff8280a63f>] __wait_for_common kernel/sched/completion.c:93 [inline]
 [<ffffffff8280a63f>] wait_for_common+0x3ef/0x5d0 kernel/sched/completion.c:101
 [<ffffffff8280a838>] wait_for_completion+0x18/0x20 kernel/sched/completion.c:122
 [<ffffffff81243b37>] __wait_rcu_gp+0x137/0x1b0 kernel/rcu/update.c:369
 [<ffffffff8124c21a>] synchronize_rcu.part.55+0xfa/0x110 kernel/rcu/tree_plugin.h:684
 [<ffffffff8124c257>] synchronize_rcu+0x27/0x90 kernel/rcu/tree_plugin.h:685
 [<ffffffff815750c7>] kern_unmount+0x57/0xd0 fs/namespace.c:3344
 [<ffffffff8165e357>] pid_ns_release_proc+0x37/0x50 fs/proc/root.c:227
 [<ffffffff812ec609>] proc_cleanup_work+0x19/0x20 kernel/pid_namespace.c:76
 [<ffffffff81131001>] process_one_work+0x831/0x15f0 kernel/workqueue.c:2092
 [<ffffffff81131e96>] worker_thread+0xd6/0x1140 kernel/workqueue.c:2226
 [<ffffffff81142c3d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff82817a5c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
2 locks held by kworker/0:0/4:
 #0:  ("events"){.+.+.+}, at: [<ffffffff81130f0c>] process_one_work+0x73c/0x15f0 kernel/workqueue.c:2085
 #1:  ((&ns->proc_work)){+.+...}, at: [<ffffffff81130f44>] process_one_work+0x774/0x15f0 kernel/workqueue.c:2089
2 locks held by khungtaskd/24:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8131c0cc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8131c0cc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff813fe63f>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
1 lock held by oom_reaper/25:
 #0:  (oom_lock){+.+...}, at: [<ffffffff814194d0>] __oom_reap_task_mm+0xd0/0x560 mm/oom_kill.c:487
1 lock held by rsyslogd/1914:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff8156cc7c>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by cron/1964:
 #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810b29a2>] __do_page_fault+0x272/0xa60 arch/x86/mm/fault.c:1335
 #1:  (&ei->i_mmap_sem){++++.+}, at: [<ffffffff816e7716>] ext4_filemap_fault+0x66/0xa0 fs/ext4/inode.c:5852
2 locks held by getty/2041:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff82815952>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff81d37362>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
2 locks held by syz-fuzzer/2071:
 #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810b29a2>] __do_page_fault+0x272/0xa60 arch/x86/mm/fault.c:1335
 #1:  (&ei->i_mmap_sem){++++.+}, at: [<ffffffff816e7716>] ext4_filemap_fault+0x66/0xa0 fs/ext4/inode.c:5852
2 locks held by syz-fuzzer/2072:
 #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810b29a2>] __do_page_fault+0x272/0xa60 arch/x86/mm/fault.c:1335
 #1:  (&ei->i_mmap_sem){++++.+}, at: [<ffffffff816e7716>] ext4_filemap_fault+0x66/0xa0 fs/ext4/inode.c:5852
2 locks held by syz-fuzzer/2077:
 #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810b29a2>] __do_page_fault+0x272/0xa60 arch/x86/mm/fault.c:1335
 #1:  (&ei->i_mmap_sem){++++.+}, at: [<ffffffff816e7716>] ext4_filemap_fault+0x66/0xa0 fs/ext4/inode.c:5852
2 locks held by syz-executor.3/2780:
 #0:  (&type->s_umount_key#42){++++..}, at: [<ffffffff81514519>] deactivate_super+0x89/0xd0 fs/super.c:340
 #1:  (shrinker_rwsem){++++..}, at: [<ffffffff81449728>] unregister_shrinker+0x58/0x230 mm/vmscan.c:300
3 locks held by kworker/u4:13/5489:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81130f0c>] process_one_work+0x73c/0x15f0 kernel/workqueue.c:2085
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff81130f44>] process_one_work+0x774/0x15f0 kernel/workqueue.c:2089
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff822e681f>] cleanup_net+0x13f/0x8b0 net/core/net_namespace.c:439
2 locks held by kworker/0:3/8300:
 #0:  ("events"){.+.+.+}, at: [<ffffffff81130f0c>] process_one_work+0x73c/0x15f0 kernel/workqueue.c:2085
 #1:  ((&ns->proc_work)){+.+...}, at: [<ffffffff81130f44>] process_one_work+0x774/0x15f0 kernel/workqueue.c:2089
2 locks held by kworker/0:1/824:
 #0:  ("events"){.+.+.+}, at: [<ffffffff81130f0c>] process_one_work+0x73c/0x15f0 kernel/workqueue.c:2085
 #1:  ((&ns->proc_work)){+.+...}, at: [<ffffffff81130f44>] process_one_work+0x774/0x15f0 kernel/workqueue.c:2089

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 24 Comm: khungtaskd Not tainted 4.9.141+ #1
 ffff8801d9907d08 ffffffff81b42e79 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810983b0 ffff8801d9907d40
 ffffffff81b4df89 0000000000000001 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81b42e79>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b42e79>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81b4df89>] nmi_cpu_backtrace.cold.0+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81b4df1c>] nmi_trigger_cpumask_backtrace+0x12c/0x151 lib/nmi_backtrace.c:60
 [<ffffffff810984b4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff8131c65d>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff8131c65d>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8131c65d>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8131c65d>] watchdog+0x6ad/0xa20 kernel/hung_task.c:239
 [<ffffffff81142c3d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff82817a5c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 12058 Comm: syz-executor.3 Not tainted 4.9.141+ #1
task: ffff88006de8df00 task.stack: ffff8800640a0000
RIP: 0010:[<ffffffff81456249>] 
c [<ffffffff81456249>] do_try_to_free_pages mm/vmscan.c:2814 [inline]
RIP: 0010:[<ffffffff81456249>] 
c [<ffffffff81456249>] try_to_free_pages+0x4f9/0xb80 mm/vmscan.c:3002
RSP: 0000:ffff8800640a7870  EFLAGS: 00000293
RAX: ffff88006de8df00 RBX: 000000000000000a RCX: 1ffff1000c814efb
RDX: 0000000000000000 RSI: ffffffff81456249 RDI: ffffffff833d4468
RBP: ffff8800640a7990 R08: ffff88021fffd018 R09: 000000000000000a
R10: ffffed0043fffa01 R11: 000000c8c5c5ce5e R12: 0000000000000000
R13: 0000000000000020 R14: ffff8800640a7968 R15: dffffc0000000000
FS:  00007f01306b7700(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001422020 CR3: 0000000197041000 CR4: 00000000001606b0
Stack:
 ffffffff833d4448
c 1ffff1000c814f19
c 0000000c00000000
c fffffbfff067a889
c
 ffff8800640a78e8
c fffffbfff0845234
c 0000000000000000
c 0000000000000000
c
 026040c00367bd1d
c ffffffff833d3600
c ffffffff833d4440
c 0000000041b58ab3
c
Call Trace:
 [<ffffffff81428a01>] __perform_reclaim mm/page_alloc.c:3324 [inline]
 [<ffffffff81428a01>] __alloc_pages_direct_reclaim mm/page_alloc.c:3345 [inline]
 [<ffffffff81428a01>] __alloc_pages_slowpath mm/page_alloc.c:3697 [inline]
 [<ffffffff81428a01>] __alloc_pages_nodemask+0x981/0x1bd0 mm/page_alloc.c:3862
 [<ffffffff814eb7e7>] __alloc_pages include/linux/gfp.h:433 [inline]
 [<ffffffff814eb7e7>] __alloc_pages_node include/linux/gfp.h:446 [inline]
 [<ffffffff814eb7e7>] alloc_slab_page mm/slub.c:1408 [inline]
 [<ffffffff814eb7e7>] allocate_slab mm/slub.c:1557 [inline]
 [<ffffffff814eb7e7>] new_slab+0x367/0x3d0 mm/slub.c:1635
 [<ffffffff814ed97d>] new_slab_objects mm/slub.c:2419 [inline]
 [<ffffffff814ed97d>] ___slab_alloc.constprop.33+0x2ed/0x470 mm/slub.c:2576
 [<ffffffff814edb50>] __slab_alloc.isra.25.constprop.32+0x50/0xa0 mm/slub.c:2618
 [<ffffffff814eddb2>] slab_alloc_node mm/slub.c:2681 [inline]
 [<ffffffff814eddb2>] slab_alloc mm/slub.c:2723 [inline]
 [<ffffffff814eddb2>] kmem_cache_alloc+0x212/0x2b0 mm/slub.c:2728
 [<ffffffff8153eca8>] getname_flags+0xc8/0x550 fs/namei.c:137
 [<ffffffff8153fa2f>] user_path_at_empty+0x2f/0x70 fs/namei.c:2578
 [<ffffffff81586af2>] user_path_at include/linux/namei.h:55 [inline]
 [<ffffffff81586af2>] path_setxattr+0xb2/0x180 fs/xattr.c:463
 [<ffffffff81586fb8>] SYSC_lsetxattr fs/xattr.c:490 [inline]
 [<ffffffff81586fb8>] SyS_lsetxattr+0x38/0x50 fs/xattr.c:486
 [<ffffffff810056ef>] do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
 [<ffffffff82817893>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c