======================================
| [  121.583801][   T12] ==================================================================
| [  121.584281][   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)
| [  121.584693][   T12] Write of size 8 at addr 0000000000000000 by task kworker/u16:0/12
| [  121.585104][   T12]
[  121.585263][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  121.585267][   T12] Workqueue: netns cleanup_net
[  121.585282][   T12] Call Trace:
[  121.585285][   T12]  <TASK>
[  121.585288][   T12]  dump_stack_lvl (lib/dump_stack.c:123)
[  121.585299][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  121.585306][   T12]  kasan_report (mm/kasan/report.c:597)
[  121.585317][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  121.585324][   T12]  kasan_check_range (mm/kasan/generic.c:194 mm/kasan/generic.c:200)
[  121.585330][   T12]  try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[  121.585337][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  121.585342][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  121.585348][   T12]  ? queue_delayed_work_on (kernel/workqueue.c:2590)
[  121.585353][   T12]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[  121.585362][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  121.585368][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  121.585375][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  121.585380][   T12]  ? __local_bh_enable_ip (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:119 kernel/softirq.c:455)
[  121.585387][   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)
[  121.585393][   T12]  ? netif_set_allmulti (net/core/dev.c:9890)
[  121.585399][   T12]  ? trace_contention_end (./include/trace/events/lock.h:122 (discriminator 21))
[  121.585407][   T12]  netif_change_flags (net/core/dev.c:9989)
[  121.585413][   T12]  dev_change_flags (./include/net/netdev_lock.h:30 ./include/net/netdev_lock.h:47 net/core/dev_api.c:69)
[  121.585419][   T12]  cycle_netdev (drivers/net/vrf.c:1052)
[  121.585427][   T12]  vrf_dellink (drivers/net/vrf.c:1671)
[  121.585431][   T12]  ? vrf_map_unregister_dev (drivers/net/vrf.c:1667)
[  121.585440][   T12]  default_device_exit_batch (net/core/dev.c:13221 (discriminator 2))
[  121.585445][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[  121.585452][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[  121.585460][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[  121.585465][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  121.585473][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  121.585479][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  121.585485][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  121.585495][   T12]  process_one_work (kernel/workqueue.c:3268)
[  121.585505][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  121.585513][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  121.585519][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  121.585528][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  121.585533][   T12]  kthread (kernel/kthread.c:463)
[  121.585541][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  121.585546][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  121.585552][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  121.585559][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  121.585564][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  121.585571][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  121.585574][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  121.585579][   T12]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [  121.597604][   T12] #PF: error_code(0x0002) - not-present page
| [  121.597841][   T12] PGD 0 P4D 0
| [  121.597985][   T12] Oops: Oops: 0002 [#1] SMP KASAN
| [  121.598823][   T12] Tainted: [B]=BAD_PAGE
[  121.598961][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  121.599192][   T12] Workqueue: netns cleanup_net
[  121.599389][   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)
[  121.599627][   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
[  121.600380][   T12] RSP: 0018:ffffc900000c7698 EFLAGS: 00010046
[  121.600732][   T12] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff94249b8a
[  121.601010][   T12] RDX: fffffbfff31ecacd RSI: 0000000000000008 RDI: ffffffff98f65660
[  121.601381][   T12] RBP: ffffc900000c7700 R08: 0000000000000001 R09: fffffbfff31ecacc
[  121.601657][   T12] R10: ffffffff98f65667 R11: ffffc900000c7180 R12: 0000000000000000
[  121.602042][   T12] R13: 0000000000000282 R14: ffff888008bf9000 R15: dffffc0000000000
[  121.602312][   T12] FS:  0000000000000000(0000) GS:ffff8880d4207000(0000) knlGS:0000000000000000
[  121.602629][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  121.602862][   T12] CR2: 0000000000000000 CR3: 0000000004a07004 CR4: 0000000000772ef0
[  121.603134][   T12] PKRU: 55555554
[  121.603284][   T12] Call Trace:
[  121.603418][   T12]  <TASK>
[  121.603513][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[  121.603703][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[  121.604021][   T12]  ? queue_delayed_work_on (kernel/workqueue.c:2590)
[  121.604197][   T12]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[  121.604386][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[  121.604678][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[  121.604886][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[  121.605114][   T12]  ? __local_bh_enable_ip (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:119 kernel/softirq.c:455)
[  121.605346][   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)
[  121.605584][   T12]  ? netif_set_allmulti (net/core/dev.c:9890)
[  121.605776][   T12]  ? trace_contention_end (./include/trace/events/lock.h:122 (discriminator 21))
[  121.605975][   T12]  netif_change_flags (net/core/dev.c:9989)
[  121.606154][   T12]  dev_change_flags (./include/net/netdev_lock.h:30 ./include/net/netdev_lock.h:47 net/core/dev_api.c:69)
[  121.606353][   T12]  cycle_netdev (drivers/net/vrf.c:1052)
[  121.606494][   T12]  vrf_dellink (drivers/net/vrf.c:1671)
[  121.606649][   T12]  ? vrf_map_unregister_dev (drivers/net/vrf.c:1667)
[  121.606832][   T12]  default_device_exit_batch (net/core/dev.c:13221 (discriminator 2))
[  121.607011][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[  121.607193][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[  121.607483][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[  121.607677][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[  121.607990][   T12]  cleanup_net (net/core/net_namespace.c:698)
[  121.608172][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[  121.608357][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  121.608585][   T12]  process_one_work (kernel/workqueue.c:3268)
[  121.608890][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[  121.609071][   T12]  ? assign_work (kernel/workqueue.c:1206)
[  121.609248][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[  121.609432][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[  121.609740][   T12]  kthread (kernel/kthread.c:463)
[  121.609882][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  121.610159][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[  121.610338][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[  121.610514][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[  121.610707][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[  121.610896][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[  121.611072][   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