======================================
| [  116.360540][   T12] ==================================================================
| [  116.360939][   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)
| [  116.361255][   T12] Write of size 8 at addr 0000000000000000 by task kworker/u16:0/12
| [  116.361542][   T12]
[  116.361654][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  116.361660][   T12] Workqueue: netns cleanup_net
[  116.361680][   T12] Call Trace:
[  116.361686][   T12]  <TASK>
[  116.361688][   T12]  dump_stack_lvl (lib/dump_stack.c:123)
[  116.361703][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  116.361707][   T12]  kasan_report (mm/kasan/report.c:597)
[  116.361720][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  116.361726][   T12]  kasan_check_range (mm/kasan/generic.c:194 mm/kasan/generic.c:200)
[  116.361732][   T12]  try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  116.361737][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  116.361740][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  116.361745][   T12]  ? queue_delayed_work_on (kernel/workqueue.c:2590)
[  116.361748][   T12]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[  116.361764][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  116.361768][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  116.361775][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  116.361781][   T12]  ? __local_bh_enable_ip (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:119 kernel/softirq.c:455)
[  116.361789][   T12]  __dev_change_flags (./include/linux/list.h:119 ./include/linux/list.h:223 ./include/linux/list.h:237 net/core/dev.c:1945 net/core/dev.c:9924)
[  116.361797][   T12]  ? netif_set_allmulti (net/core/dev.c:9890)
[  116.361803][   T12]  ? trace_contention_end (./include/trace/events/lock.h:122 (discriminator 21))
[  116.361815][   T12]  netif_change_flags (net/core/dev.c:9989)
[  116.361820][   T12]  dev_change_flags (./include/net/netdev_lock.h:30 ./include/net/netdev_lock.h:47 net/core/dev_api.c:69)
[  116.361825][   T12]  cycle_netdev (drivers/net/vrf.c:1052)
[  116.361835][   T12]  vrf_dellink (drivers/net/vrf.c:1671)
[  116.361838][   T12]  ? vrf_map_unregister_dev (drivers/net/vrf.c:1667)
[  116.361844][   T12]  default_device_exit_batch (net/core/dev.c:13221 (discriminator 2))
[  116.361848][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[  116.361858][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[  116.361867][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[  116.361871][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  116.361877][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  116.361881][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  116.361886][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  116.361896][   T12]  process_one_work (kernel/workqueue.c:3268)
[  116.361903][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  116.361909][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  116.361913][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  116.361919][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  116.361923][   T12]  kthread (kernel/kthread.c:463)
[  116.361929][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  116.361932][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  116.361943][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  116.361947][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  116.361950][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  116.361954][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  116.361957][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  116.361960][   T12]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [  116.372278][   T12] #PF: error_code(0x0002) - not-present page
| [  116.372518][   T12] PGD 0 P4D 0
| [  116.372659][   T12] Oops: Oops: 0002 [#1] SMP KASAN
| [  116.373278][   T12] Tainted: [B]=BAD_PAGE
[  116.373421][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  116.373657][   T12] Workqueue: netns cleanup_net
[  116.373860][   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)
[  116.374098][   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
[  116.374768][   T12] RSP: 0018:ffffc900000c7698 EFLAGS: 00010046
[  116.375010][   T12] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8da49b8a
[  116.375285][   T12] RDX: fffffbfff24ecacd RSI: 0000000000000008 RDI: ffffffff92765660
[  116.375570][   T12] RBP: ffffc900000c7700 R08: 0000000000000001 R09: fffffbfff24ecacc
[  116.375847][   T12] R10: ffffffff92765667 R11: ffffc900000c7180 R12: 0000000000000000
[  116.376129][   T12] R13: 0000000000000282 R14: ffff88800f0d4000 R15: dffffc0000000000
[  116.376398][   T12] FS:  0000000000000000(0000) GS:ffff8880da987000(0000) knlGS:0000000000000000
[  116.376727][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  116.376967][   T12] CR2: 0000000000000000 CR3: 0000000049d49002 CR4: 0000000000772ef0
[  116.377250][   T12] PKRU: 55555554
[  116.377388][   T12] Call Trace:
[  116.377540][   T12]  <TASK>
[  116.377636][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  116.377828][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  116.378023][   T12]  ? queue_delayed_work_on (kernel/workqueue.c:2590)
[  116.378209][   T12]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[  116.378388][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  116.378580][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  116.378759][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  116.378953][   T12]  ? __local_bh_enable_ip (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:119 kernel/softirq.c:455)
[  116.379137][   T12]  __dev_change_flags (./include/linux/list.h:119 ./include/linux/list.h:223 ./include/linux/list.h:237 net/core/dev.c:1945 net/core/dev.c:9924)
[  116.379321][   T12]  ? netif_set_allmulti (net/core/dev.c:9890)
[  116.379516][   T12]  ? trace_contention_end (./include/trace/events/lock.h:122 (discriminator 21))
[  116.379694][   T12]  netif_change_flags (net/core/dev.c:9989)
[  116.379886][   T12]  dev_change_flags (./include/net/netdev_lock.h:30 ./include/net/netdev_lock.h:47 net/core/dev_api.c:69)
[  116.380073][   T12]  cycle_netdev (drivers/net/vrf.c:1052)
[  116.380208][   T12]  vrf_dellink (drivers/net/vrf.c:1671)
[  116.380344][   T12]  ? vrf_map_unregister_dev (drivers/net/vrf.c:1667)
[  116.380652][   T12]  default_device_exit_batch (net/core/dev.c:13221 (discriminator 2))
[  116.380841][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[  116.381035][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[  116.381218][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[  116.381393][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  116.381589][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  116.381770][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  116.381966][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  116.382266][   T12]  process_one_work (kernel/workqueue.c:3268)
[  116.382457][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  116.382646][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  116.382833][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  116.383131][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  116.383310][   T12]  kthread (kernel/kthread.c:463)
[  116.383453][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  116.383640][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  116.383956][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  116.384144][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  116.384324][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  116.384526][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  116.384836][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)


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