======================================
| [  104.208629][   T12] ==================================================================
| [  104.208965][   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)
| [  104.209276][   T12] Write of size 8 at addr 0000000000000000 by task kworker/u16:0/12
| [  104.209577][   T12]
[  104.209687][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  104.209690][   T12] Workqueue: netns cleanup_net
[  104.209712][   T12] Call Trace:
[  104.209714][   T12]  <TASK>
[  104.209717][   T12]  dump_stack_lvl (lib/dump_stack.c:123)
[  104.209725][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  104.209728][   T12]  kasan_report (mm/kasan/report.c:597)
[  104.209736][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  104.209741][   T12]  kasan_check_range (mm/kasan/generic.c:194 mm/kasan/generic.c:200)
[  104.209744][   T12]  try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  104.209746][   T12]  ? __ipv6_dev_mc_dec (net/ipv6/mcast.c:1008)
[  104.209754][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  104.209757][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  104.209760][   T12]  ? br_multicast_leave_snoopers (net/bridge/br_multicast.c:4220) bridge
[  104.209798][   T12]  ? br_multicast_join_snoopers (net/bridge/br_multicast.c:4220) bridge
[  104.209829][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  104.209833][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  104.209838][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  104.209841][   T12]  ? netif_close_many (net/core/dev.c:1959)
[  104.209845][   T12]  netif_close_many (net/core/dev.c:1959)
[  104.209848][   T12]  ? find_held_lock (kernel/locking/lockdep.c:5350)
[  104.209853][   T12]  ? __dev_close_many (net/core/dev.c:1949)
[  104.209856][   T12]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[  104.209861][   T12]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[  104.209865][   T12]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[  104.209869][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[  104.209873][   T12]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[  104.209876][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[  104.209880][   T12]  ? br_dev_delete (net/bridge/br_if.c:397) bridge
[  104.209911][   T12]  ops_undo_list (net/core/net_namespace.c:189 net/core/net_namespace.c:248)
[  104.209917][   T12]  ? netns_get (net/core/net_namespace.c:223)
[  104.209920][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  104.209925][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  104.209928][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  104.209931][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  104.209937][   T12]  process_one_work (kernel/workqueue.c:3268)
[  104.209943][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  104.209949][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  104.209952][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  104.209958][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  104.209961][   T12]  kthread (kernel/kthread.c:463)
[  104.209964][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  104.209967][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  104.209972][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  104.209976][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  104.209979][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  104.209983][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  104.209986][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  104.209989][   T12]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [  104.220792][   T12] #PF: error_code(0x0002) - not-present page
| [  104.220998][   T12] PGD 0 P4D 0
| [  104.221131][   T12] Oops: Oops: 0002 [#1] SMP KASAN
| [  104.221786][   T12] Tainted: [B]=BAD_PAGE
[  104.221924][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  104.222144][   T12] Workqueue: netns cleanup_net
[  104.222428][   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)
[  104.222643][   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 df 81 84 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 df 81 84 00       	call   0x848209
  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
[  104.223358][   T12] RSP: 0018:ffffc900000c7730 EFLAGS: 00010046
[  104.223575][   T12] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffb7840aaa
[  104.223940][   T12] RDX: fffffbfff774fecd RSI: 0000000000000008 RDI: ffffffffbba7f660
[  104.224207][   T12] RBP: ffffc900000c7798 R08: 0000000000000001 R09: fffffbfff774fecc
[  104.224467][   T12] R10: ffffffffbba7f667 R11: ffffc900000c7200 R12: 0000000000000000
[  104.224826][   T12] R13: 0000000000000286 R14: ffff88800dd5a000 R15: dffffc0000000000
[  104.225071][   T12] FS:  0000000000000000(0000) GS:ffff88807a86c000(0000) knlGS:0000000000000000
[  104.225471][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  104.225699][   T12] CR2: 0000000000000000 CR3: 0000000023d35001 CR4: 0000000000772ef0
[  104.225940][   T12] PKRU: 55555554
[  104.226066][   T12] Call Trace:
[  104.226297][   T12]  <TASK>
[  104.226380][   T12]  ? __ipv6_dev_mc_dec (net/ipv6/mcast.c:1008)
[  104.226558][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  104.226729][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  104.226894][   T12]  ? br_multicast_leave_snoopers (net/bridge/br_multicast.c:4220) bridge
[  104.227134][   T12]  ? br_multicast_join_snoopers (net/bridge/br_multicast.c:4220) bridge
[  104.227372][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  104.227553][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  104.227821][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  104.227986][   T12]  ? netif_close_many (net/core/dev.c:1959)
[  104.228171][   T12]  netif_close_many (net/core/dev.c:1959)
[  104.228352][   T12]  ? find_held_lock (kernel/locking/lockdep.c:5350)
[  104.228616][   T12]  ? __dev_close_many (net/core/dev.c:1949)
[  104.228782][   T12]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[  104.228982][   T12]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[  104.229212][   T12]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[  104.229481][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[  104.229655][   T12]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[  104.229845][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[  104.230012][   T12]  ? br_dev_delete (net/bridge/br_if.c:397) bridge
[  104.230305][   T12]  ops_undo_list (net/core/net_namespace.c:189 net/core/net_namespace.c:248)
[  104.230481][   T12]  ? netns_get (net/core/net_namespace.c:223)
[  104.230647][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  104.230815][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  104.231071][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  104.231238][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  104.231414][   T12]  process_one_work (kernel/workqueue.c:3268)
[  104.231593][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  104.231856][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  104.232020][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  104.232202][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  104.232374][   T12]  kthread (kernel/kthread.c:463)
[  104.232604][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  104.232796][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  104.232966][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  104.233140][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  104.233408][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  104.233585][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  104.233781][   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