======================================
| [   47.081817][   T71] ==================================================================
| [   47.082092][   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)
| [   47.082380][   T71] Write of size 8 at addr 0000000000000000 by task kworker/u16:1/71
| [   47.082619][   T71]
[   47.082721][   T71] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   47.082726][   T71] Workqueue: netns cleanup_net
[   47.082750][   T71] Call Trace:
[   47.082754][   T71]  <TASK>
[   47.082756][   T71]  dump_stack_lvl (lib/dump_stack.c:123)
[   47.082772][   T71]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   47.082775][   T71]  kasan_report (mm/kasan/report.c:597)
[   47.082791][   T71]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   47.082797][   T71]  kasan_check_range (mm/kasan/generic.c:194 mm/kasan/generic.c:200)
[   47.082801][   T71]  try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   47.082804][   T71]  ? __ipv6_dev_mc_dec (net/ipv6/mcast.c:1008)
[   47.082814][   T71]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[   47.082818][   T71]  ? enable_delayed_work (kernel/workqueue.c:4359)
[   47.082822][   T71]  ? br_multicast_leave_snoopers (net/bridge/br_multicast.c:4220)
[   47.082829][   T71]  ? br_multicast_join_snoopers (net/bridge/br_multicast.c:4220)
[   47.082834][   T71]  __cancel_work_sync (kernel/workqueue.c:4383)
[   47.082838][   T71]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[   47.082846][   T71]  ? netdev_notify_peers (net/core/dev.c:1891)
[   47.082849][   T71]  ? netif_close_many (net/core/dev.c:1959)
[   47.082853][   T71]  netif_close_many (net/core/dev.c:1959)
[   47.082857][   T71]  ? find_held_lock (kernel/locking/lockdep.c:5350)
[   47.082865][   T71]  ? __dev_close_many (net/core/dev.c:1949)
[   47.082868][   T71]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[   47.082873][   T71]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[   47.082877][   T71]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[   47.082894][   T71]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   47.082901][   T71]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[   47.082904][   T71]  ? unregister_netdevice_many (net/core/dev.c:12441)
[   47.082909][   T71]  ? br_dev_delete (net/bridge/br_if.c:397)
[   47.082916][   T71]  ops_undo_list (net/core/net_namespace.c:189 net/core/net_namespace.c:248)
[   47.082921][   T71]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[   47.082925][   T71]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[   47.082931][   T71]  cleanup_net (net/core/net_namespace.c:698)
[   47.082935][   T71]  ? net_passive_dec (net/core/net_namespace.c:660)
[   47.082940][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   47.082949][   T71]  process_one_work (kernel/workqueue.c:3268)
[   47.082956][   T71]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   47.082962][   T71]  ? assign_work (kernel/workqueue.c:1206)
[   47.082967][   T71]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   47.082973][   T71]  ? rescuer_thread (kernel/workqueue.c:3373)
[   47.082976][   T71]  kthread (kernel/kthread.c:463)
[   47.082983][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   47.082985][   T71]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   47.082997][   T71]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   47.083001][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   47.083004][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   47.083008][   T71]  ret_from_fork (arch/x86/kernel/process.c:164)
[   47.083011][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   47.083014][   T71]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [   47.092587][   T71] #PF: error_code(0x0002) - not-present page
| [   47.092789][   T71] PGD 0 P4D 0
| [   47.092918][   T71] Oops: Oops: 0002 [#1] SMP KASAN
| [   47.093574][   T71] Tainted: [B]=BAD_PAGE
[   47.093696][   T71] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   47.093994][   T71] Workqueue: netns cleanup_net
[   47.094175][   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)
[   47.094396][   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 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
[   47.095060][   T71] RSP: 0018:ffffc900004c7720 EFLAGS: 00010046
[   47.095274][   T71] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffa6849b8a
[   47.095560][   T71] RDX: fffffbfff56acacd RSI: 0000000000000008 RDI: ffffffffab565660
[   47.095802][   T71] RBP: ffffc900004c7788 R08: 0000000000000001 R09: fffffbfff56acacc
[   47.096147][   T71] R10: ffffffffab565667 R11: ffffc900004c7200 R12: 0000000000000000
[   47.096415][   T71] R13: 0000000000000282 R14: ffff88800b8d2000 R15: dffffc0000000000
[   47.096659][   T71] FS:  0000000000000000(0000) GS:ffff8880c1c87000(0000) knlGS:0000000000000000
[   47.097057][   T71] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   47.097289][   T71] CR2: 0000000000000000 CR3: 0000000026949003 CR4: 0000000000772ef0
[   47.097535][   T71] PKRU: 55555554
[   47.097752][   T71] Call Trace:
[   47.097886][   T71]  <TASK>
[   47.097974][   T71]  ? __ipv6_dev_mc_dec (net/ipv6/mcast.c:1008)
[   47.098152][   T71]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[   47.098324][   T71]  ? enable_delayed_work (kernel/workqueue.c:4359)
[   47.098579][   T71]  ? br_multicast_leave_snoopers (net/bridge/br_multicast.c:4220)
[   47.098781][   T71]  ? br_multicast_join_snoopers (net/bridge/br_multicast.c:4220)
[   47.098981][   T71]  __cancel_work_sync (kernel/workqueue.c:4383)
[   47.099237][   T71]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[   47.099412][   T71]  ? netdev_notify_peers (net/core/dev.c:1891)
[   47.099571][   T71]  ? netif_close_many (net/core/dev.c:1959)
[   47.099736][   T71]  netif_close_many (net/core/dev.c:1959)
[   47.099990][   T71]  ? find_held_lock (kernel/locking/lockdep.c:5350)
[   47.100157][   T71]  ? __dev_close_many (net/core/dev.c:1949)
[   47.100323][   T71]  ? netif_close_many_and_unlock (net/core/dev.c:12476)
[   47.100522][   T71]  unregister_netdevice_many_notify (net/core/dev.c:12545)
[   47.100815][   T71]  ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4472)
[   47.100983][   T71]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   47.101144][   T71]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[   47.101317][   T71]  ? unregister_netdevice_many (net/core/dev.c:12441)
[   47.101570][   T71]  ? br_dev_delete (net/bridge/br_if.c:397)
[   47.101738][   T71]  ops_undo_list (net/core/net_namespace.c:189 net/core/net_namespace.c:248)
[   47.101904][   T71]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[   47.102064][   T71]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[   47.102333][   T71]  cleanup_net (net/core/net_namespace.c:698)
[   47.102493][   T71]  ? net_passive_dec (net/core/net_namespace.c:660)
[   47.102653][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   47.102817][   T71]  process_one_work (kernel/workqueue.c:3268)
[   47.103073][   T71]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   47.103238][   T71]  ? assign_work (kernel/workqueue.c:1206)
[   47.103402][   T71]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   47.103565][   T71]  ? rescuer_thread (kernel/workqueue.c:3373)
[   47.103827][   T71]  kthread (kernel/kthread.c:463)
[   47.103950][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   47.104108][   T71]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   47.104280][   T71]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   47.104534][   T71]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   47.104696][   T71]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   47.104855][   T71]  ret_from_fork (arch/x86/kernel/process.c:164)
[   47.105014][   T71]  ? 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