======================================
| [   26.842513][   T71] ==================================================================
| [   26.843011][   T71] BUG: KASAN: null-ptr-deref in try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
| [   26.843390][   T71] Write of size 8 at addr 0000000000000000 by task kworker/u16:1/71
| [   26.843784][   T71]
[   26.843915][   T71] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   26.843921][   T71] Workqueue: netns cleanup_net
[   26.843949][   T71] Call Trace:
[   26.843953][   T71]  <TASK>
[   26.843956][   T71]  dump_stack_lvl (lib/dump_stack.c:123)
[   26.843978][   T71]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   26.843985][   T71]  kasan_report (mm/kasan/report.c:597)
[   26.844000][   T71]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   26.844006][   T71]  kasan_check_range (mm/kasan/generic.c:194 mm/kasan/generic.c:200)
[   26.844010][   T71]  try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   26.844015][   T71]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[   26.844018][   T71]  ? enable_delayed_work (kernel/workqueue.c:4359)
[   26.844023][   T71]  ? qdisc_destroy (net/sched/sch_generic.c:1355)
[   26.844036][   T71]  __cancel_work_sync (kernel/workqueue.c:4383)
[   26.844040][   T71]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[   26.844049][   T71]  ? netdev_notify_peers (net/core/dev.c:1891)
[   26.844053][   T71]  ? netif_close_many (net/core/dev.c:1959)
[   26.844058][   T71]  netif_close_many (net/core/dev.c:1959)
[   26.844062][   T71]  ? __mutex_handoff (kernel/locking/mutex.c:88)
[   26.844072][   T71]  ? __dev_close_many (net/core/dev.c:1949)
[   26.844076][   T71]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[   26.844081][   T71]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[   26.844085][   T71]  ? find_held_lock (kernel/locking/lockdep.c:5350)
[   26.844089][   T71]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   26.844095][   T71]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[   26.844098][   T71]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   26.844100][   T71]  ? unregister_netdevice_queue (net/core/dev.c:12442)
[   26.844102][   T71]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[   26.844110][   T71]  ? unregister_netdevice_many (net/core/dev.c:12441)
[   26.844116][   T71]  default_device_exit_batch (net/core/dev.c:13229)
[   26.844120][   T71]  ? unregister_netdev (net/core/dev.c:13204)
[   26.844126][   T71]  ops_undo_list (net/core/net_namespace.c:251)
[   26.844132][   T71]  ? netns_get (net/core/net_namespace.c:223)
[   26.844134][   T71]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[   26.844140][   T71]  cleanup_net (net/core/net_namespace.c:698)
[   26.844150][   T71]  ? net_passive_dec (net/core/net_namespace.c:660)
[   26.844154][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   26.844162][   T71]  process_one_work (kernel/workqueue.c:3268)
[   26.844169][   T71]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   26.844175][   T71]  ? assign_work (kernel/workqueue.c:1206)
[   26.844179][   T71]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   26.844187][   T71]  ? rescuer_thread (kernel/workqueue.c:3373)
[   26.844191][   T71]  kthread (kernel/kthread.c:463)
[   26.844197][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   26.844200][   T71]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   26.844211][   T71]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   26.844218][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   26.844223][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   26.844228][   T71]  ret_from_fork (arch/x86/kernel/process.c:164)
[   26.844231][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   26.844234][   T71]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [   26.857465][   T71] #PF: error_code(0x0002) - not-present page
| [   26.857716][   T71] PGD 0 P4D 0
| [   26.857885][   T71] Oops: Oops: 0002 [#1] SMP KASAN
| [   26.858701][   T71] Tainted: [B]=BAD_PAGE
[   26.858887][   T71] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   26.859288][   T71] Workqueue: netns cleanup_net
[   26.859505][   T71] RIP: 0010:try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   26.859757][   T71] Code: 00 41 89 c0 b8 01 00 00 00 45 85 c0 74 0f 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3 be 08 00 00 00 48 89 df e8 6f 7d 81 00 <f0> 48 0f ba 2b 00 72 11 48 83 c4 10 31 c0 5b 5d 41 5c 41 5d 41 5e
All code
========
   0:	00 41 89             	add    %al,-0x77(%rcx)
   3:	c0 b8 01 00 00 00 45 	sarb   $0x45,0x1(%rax)
   a:	85 c0                	test   %eax,%eax
   c:	74 0f                	je     0x1d
   e:	48 83 c4 10          	add    $0x10,%rsp
  12:	5b                   	pop    %rbx
  13:	5d                   	pop    %rbp
  14:	41 5c                	pop    %r12
  16:	41 5d                	pop    %r13
  18:	41 5e                	pop    %r14
  1a:	41 5f                	pop    %r15
  1c:	c3                   	ret
  1d:	be 08 00 00 00       	mov    $0x8,%esi
  22:	48 89 df             	mov    %rbx,%rdi
  25:	e8 6f 7d 81 00       	call   0x817d99
  2a:*	f0 48 0f ba 2b 00    	lock btsq $0x0,(%rbx)		<-- trapping instruction
  30:	72 11                	jb     0x43
  32:	48 83 c4 10          	add    $0x10,%rsp
  36:	31 c0                	xor    %eax,%eax
  38:	5b                   	pop    %rbx
  39:	5d                   	pop    %rbp
  3a:	41 5c                	pop    %r12
  3c:	41 5d                	pop    %r13
  3e:	41 5e                	pop    %r14

Code starting with the faulting instruction
===========================================
   0:	f0 48 0f ba 2b 00    	lock btsq $0x0,(%rbx)
   6:	72 11                	jb     0x19
   8:	48 83 c4 10          	add    $0x10,%rsp
   c:	31 c0                	xor    %eax,%eax
   e:	5b                   	pop    %rbx
   f:	5d                   	pop    %rbp
  10:	41 5c                	pop    %r12
  12:	41 5d                	pop    %r13
  14:	41 5e                	pop    %r14
[   26.860582][   T71] RSP: 0018:ffffc900004c7690 EFLAGS: 00010046
[   26.860833][   T71] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffa684190a
[   26.861247][   T71] RDX: fffffbfff559cecd RSI: 0000000000000008 RDI: ffffffffaace7660
[   26.861593][   T71] RBP: ffffc900004c76f8 R08: 0000000000000001 R09: fffffbfff559cecc
[   26.862075][   T71] R10: ffffffffaace7667 R11: ffffc900004c7180 R12: 0000000000000000
[   26.862409][   T71] R13: 0000000000000286 R14: ffff88800be7c000 R15: dffffc0000000000
[   26.862716][   T71] FS:  0000000000000000(0000) GS:ffff88808b704000(0000) knlGS:0000000000000000
[   26.863226][   T71] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   26.863533][   T71] CR2: 0000000000000000 CR3: 000000000a08b003 CR4: 0000000000772ef0
[   26.863874][   T71] PKRU: 55555554
[   26.864121][   T71] Call Trace:
[   26.864276][   T71]  <TASK>
[   26.864388][   T71]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[   26.864635][   T71]  ? enable_delayed_work (kernel/workqueue.c:4359)
[   26.864890][   T71]  ? qdisc_destroy (net/sched/sch_generic.c:1355)
[   26.865180][   T71]  __cancel_work_sync (kernel/workqueue.c:4383)
[   26.865409][   T71]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[   26.865644][   T71]  ? netdev_notify_peers (net/core/dev.c:1891)
[   26.865889][   T71]  ? netif_close_many (net/core/dev.c:1959)
[   26.866231][   T71]  netif_close_many (net/core/dev.c:1959)
[   26.866459][   T71]  ? __mutex_handoff (kernel/locking/mutex.c:88)
[   26.866664][   T71]  ? __dev_close_many (net/core/dev.c:1949)
[   26.866889][   T71]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[   26.867277][   T71]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[   26.867587][   T71]  ? find_held_lock (kernel/locking/lockdep.c:5350)
[   26.867800][   T71]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   26.868128][   T71]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[   26.868334][   T71]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   26.868544][   T71]  ? unregister_netdevice_queue (net/core/dev.c:12442)
[   26.868832][   T71]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[   26.869138][   T71]  ? unregister_netdevice_many (net/core/dev.c:12441)
[   26.869359][   T71]  default_device_exit_batch (net/core/dev.c:13229)
[   26.869606][   T71]  ? unregister_netdev (net/core/dev.c:13204)
[   26.869820][   T71]  ops_undo_list (net/core/net_namespace.c:251)
[   26.870110][   T71]  ? netns_get (net/core/net_namespace.c:223)
[   26.870356][   T71]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[   26.870563][   T71]  cleanup_net (net/core/net_namespace.c:698)
[   26.870777][   T71]  ? net_passive_dec (net/core/net_namespace.c:660)
[   26.871087][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   26.871306][   T71]  process_one_work (kernel/workqueue.c:3268)
[   26.871538][   T71]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   26.871742][   T71]  ? assign_work (kernel/workqueue.c:1206)
[   26.872090][   T71]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   26.872365][   T71]  ? rescuer_thread (kernel/workqueue.c:3373)
[   26.872609][   T71]  kthread (kernel/kthread.c:463)
[   26.872768][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   26.873057][   T71]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   26.873307][   T71]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   26.873536][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   26.873736][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   26.874053][   T71]  ret_from_fork (arch/x86/kernel/process.c:164)
[   26.874290][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)


Finger prints:
try_to_grab_pending:__cancel_work:__cancel_work_sync:__dev_close_many:netif_close_many
kasan_report:kasan_check_range:try_to_grab_pending:__cancel_work:__cancel_work_sync