======================================
| [  893.910546][   T12] ==================================================================
| [  893.910959][   T12] 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)
| [  893.911297][   T12] Write of size 8 at addr 0000000000000000 by task kworker/u16:0/12
| [  893.911596][   T12]
[  893.911721][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  893.911725][   T12] Workqueue: netns cleanup_net
[  893.911745][   T12] Call Trace:
[  893.911749][   T12]  <TASK>
[  893.911752][   T12]  dump_stack_lvl (lib/dump_stack.c:123)
[  893.911766][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  893.911771][   T12]  kasan_report (mm/kasan/report.c:597)
[  893.911786][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  893.911792][   T12]  kasan_check_range (mm/kasan/generic.c:194 mm/kasan/generic.c:200)
[  893.911796][   T12]  try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  893.911801][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  893.911805][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  893.911810][   T12]  ? queue_delayed_work_on (kernel/workqueue.c:2565 (discriminator 1))
[  893.911815][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  893.911820][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  893.911826][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  893.911833][   T12]  ? netif_close_many (net/core/dev.c:1959)
[  893.911839][   T12]  netif_close_many (net/core/dev.c:1959)
[  893.911843][   T12]  ? __mutex_handoff (kernel/locking/mutex.c:88)
[  893.911854][   T12]  ? __dev_close_many (net/core/dev.c:1949)
[  893.911857][   T12]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[  893.911860][   T12]  ? trace_contention_end (./include/trace/events/lock.h:122 (discriminator 21))
[  893.911864][   T12]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[  893.911870][   T12]  ? default_device_exit_batch (net/core/dev.c:13215)
[  893.911875][   T12]  ? mutex_is_locked (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-long.h:38 ./include/linux/atomic/atomic-instrumented.h:3189 kernel/locking/mutex.h:47 kernel/locking/mutex.c:67)
[  893.911879][   T12]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[  893.911882][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[  893.911887][   T12]  ? unregister_netdevice_queue (net/core/dev.c:12442)
[  893.911892][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[  893.911897][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[  893.911907][   T12]  default_device_exit_batch (net/core/dev.c:13229)
[  893.911911][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[  893.911917][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[  893.911923][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[  893.911926][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  893.911932][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  893.911937][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  893.911942][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  893.911949][   T12]  process_one_work (kernel/workqueue.c:3268)
[  893.911956][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  893.911962][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  893.911966][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  893.911973][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  893.911977][   T12]  kthread (kernel/kthread.c:463)
[  893.911982][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  893.911985][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  893.911996][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  893.912000][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  893.912004][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  893.912007][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  893.912010][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  893.912013][   T12]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [  893.923247][   T12] #PF: error_code(0x0002) - not-present page
| [  893.923485][   T12] PGD 0 P4D 0
| [  893.923643][   T12] Oops: Oops: 0002 [#1] SMP KASAN
| [  893.924287][   T12] Tainted: [B]=BAD_PAGE
[  893.924429][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  893.924695][   T12] Workqueue: netns cleanup_net
[  893.924933][   T12] 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)
[  893.925177][   T12] 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 1f 93 82 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 1f 93 82 00       	call   0x829349
  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
[  893.925877][   T12] RSP: 0018:ffffc900000c7680 EFLAGS: 00010046
[  893.926116][   T12] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8c449b8a
[  893.926400][   T12] RDX: fffffbfff222cacd RSI: 0000000000000008 RDI: ffffffff91165660
[  893.926708][   T12] RBP: ffffc900000c76e8 R08: 0000000000000001 R09: fffffbfff222cacc
[  893.927113][   T12] R10: ffffffff91165667 R11: ffffc900000c7140 R12: 0000000000000000
[  893.927392][   T12] R13: 0000000000000282 R14: ffff888009384000 R15: dffffc0000000000
[  893.927696][   T12] FS:  0000000000000000(0000) GS:ffff8880d5a07000(0000) knlGS:0000000000000000
[  893.928133][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  893.928377][   T12] CR2: 0000000000000000 CR3: 000000007c749001 CR4: 0000000000772ef0
[  893.928691][   T12] PKRU: 55555554
[  893.929048][   T12] Call Trace:
[  893.929187][   T12]  <TASK>
[  893.929282][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  893.929472][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  893.929689][   T12]  ? queue_delayed_work_on (kernel/workqueue.c:2565 (discriminator 1))
[  893.929997][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  893.930181][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  893.930364][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  893.930565][   T12]  ? netif_close_many (net/core/dev.c:1959)
[  893.930877][   T12]  netif_close_many (net/core/dev.c:1959)
[  893.931060][   T12]  ? __mutex_handoff (kernel/locking/mutex.c:88)
[  893.931303][   T12]  ? __dev_close_many (net/core/dev.c:1949)
[  893.931619][   T12]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[  893.931879][   T12]  ? trace_contention_end (./include/trace/events/lock.h:122 (discriminator 21))
[  893.932072][   T12]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[  893.932299][   T12]  ? default_device_exit_batch (net/core/dev.c:13215)
[  893.932495][   T12]  ? mutex_is_locked (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-long.h:38 ./include/linux/atomic/atomic-instrumented.h:3189 kernel/locking/mutex.h:47 kernel/locking/mutex.c:67)
[  893.932705][   T12]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[  893.932888][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[  893.933066][   T12]  ? unregister_netdevice_queue (net/core/dev.c:12442)
[  893.933282][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[  893.933461][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[  893.933651][   T12]  default_device_exit_batch (net/core/dev.c:13229)
[  893.933821][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[  893.934108][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[  893.934276][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[  893.934456][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  893.934656][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  893.934959][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  893.935152][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  893.935321][   T12]  process_one_work (kernel/workqueue.c:3268)
[  893.935562][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  893.935854][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  893.936040][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  893.936234][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  893.936403][   T12]  kthread (kernel/kthread.c:463)
[  893.936686][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  893.936909][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  893.937102][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  893.937273][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  893.937566][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  893.937772][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  893.937997][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)


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