======================================
| [   17.768733][   T12] ==================================================================
| [   17.769074][   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)
| [   17.769380][   T12] Write of size 8 at addr 0000000000000000 by task kworker/u16:0/12
| [   17.769643][   T12]
[   17.769752][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   17.769758][   T12] Workqueue: netns cleanup_net
[   17.769782][   T12] Call Trace:
[   17.769787][   T12]  <TASK>
[   17.769790][   T12]  dump_stack_lvl (lib/dump_stack.c:123)
[   17.769803][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   17.769807][   T12]  kasan_report (mm/kasan/report.c:597)
[   17.769821][   T12]  ? try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   17.769827][   T12]  kasan_check_range (mm/kasan/generic.c:194 mm/kasan/generic.c:200)
[   17.769831][   T12]  try_to_grab_pending (./arch/x86/include/asm/bitops.h:136 ./include/asm-generic/bitops/instrumented-atomic.h:72 kernel/workqueue.c:2072)
[   17.769836][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[   17.769839][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[   17.769846][   T12]  ? qdisc_destroy (net/sched/sch_generic.c:1355)
[   17.769857][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[   17.769862][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[   17.769868][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[   17.769872][   T12]  ? __mutex_lock (./arch/x86/include/asm/preempt.h:104 kernel/locking/mutex.c:739 kernel/locking/mutex.c:760)
[   17.769893][   T12]  netif_close_many (net/core/dev.c:1959)
[   17.769898][   T12]  ? ww_mutex_lock (kernel/locking/mutex.c:759)
[   17.769905][   T12]  ? __dev_close_many (net/core/dev.c:1949)
[   17.769910][   T12]  ? __mutex_handoff (kernel/locking/mutex.c:88)
[   17.769926][   T12]  netif_close_many_and_unlock (net/core/dev.c:12476)
[   17.769931][   T12]  unregister_netdevice_many_notify (net/core/dev.c:12539)
[   17.769936][   T12]  ? default_device_exit_batch (net/core/dev.c:13215)
[   17.769941][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   17.769947][   T12]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[   17.769950][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   17.769953][   T12]  ? unregister_netdevice_queue (net/core/dev.c:12442)
[   17.769956][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[   17.769962][   T12]  default_device_exit_batch (net/core/dev.c:13229)
[   17.769966][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[   17.769974][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[   17.769979][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[   17.769983][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[   17.769989][   T12]  cleanup_net (net/core/net_namespace.c:698)
[   17.769993][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[   17.769998][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   17.770007][   T12]  process_one_work (kernel/workqueue.c:3268)
[   17.770014][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   17.770019][   T12]  ? assign_work (kernel/workqueue.c:1206)
[   17.770024][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   17.770030][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[   17.770033][   T12]  kthread (kernel/kthread.c:463)
[   17.770040][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   17.770043][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   17.770054][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   17.770058][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   17.770061][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   17.770065][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[   17.770068][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   17.770071][   T12]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [   17.780396][   T12] #PF: error_code(0x0002) - not-present page
| [   17.780614][   T12] PGD 0 P4D 0
| [   17.780747][   T12] Oops: Oops: 0002 [#1] SMP KASAN
| [   17.781394][   T12] Tainted: [B]=BAD_PAGE
[   17.781525][   T12] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   17.781739][   T12] Workqueue: netns cleanup_net
[   17.782029][   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)
[   17.782268][   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
[   17.782889][   T12] RSP: 0018:ffffc900000c7630 EFLAGS: 00010046
[   17.783103][   T12] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff82c49b8a
[   17.783457][   T12] RDX: fffffbfff0f2cacd RSI: 0000000000000008 RDI: ffffffff87965660
[   17.783709][   T12] RBP: ffffc900000c7698 R08: 0000000000000001 R09: fffffbfff0f2cacc
[   17.783967][   T12] R10: ffffffff87965667 R11: ffffc900000c7100 R12: 0000000000000000
[   17.784316][   T12] R13: 0000000000000286 R14: ffff88800a6a9000 R15: dffffc0000000000
[   17.784570][   T12] FS:  0000000000000000(0000) GS:ffff8880e5787000(0000) knlGS:0000000000000000
[   17.784858][   T12] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   17.785164][   T12] CR2: 0000000000000000 CR3: 0000000030b49005 CR4: 0000000000772ef0
[   17.785408][   T12] PKRU: 55555554
[   17.785537][   T12] Call Trace:
[   17.785662][   T12]  <TASK>
[   17.785750][   T12]  __cancel_work (kernel/workqueue.c:2161 kernel/workqueue.c:4364)
[   17.785950][   T12]  ? enable_delayed_work (kernel/workqueue.c:4359)
[   17.786153][   T12]  ? qdisc_destroy (net/sched/sch_generic.c:1355)
[   17.786320][   T12]  __cancel_work_sync (kernel/workqueue.c:4383)
[   17.786595][   T12]  __dev_close_many (net/core/dev.c:1879 (discriminator 2) net/core/dev.c:1932 (discriminator 2))
[   17.786764][   T12]  ? netdev_notify_peers (net/core/dev.c:1891)
[   17.786956][   T12]  ? __mutex_lock (./arch/x86/include/asm/preempt.h:104 kernel/locking/mutex.c:739 kernel/locking/mutex.c:760)
[   17.787124][   T12]  netif_close_many (net/core/dev.c:1959)
[   17.787398][   T12]  ? ww_mutex_lock (kernel/locking/mutex.c:759)
[   17.787571][   T12]  ? __dev_close_many (net/core/dev.c:1949)
[   17.787732][   T12]  ? __mutex_handoff (kernel/locking/mutex.c:88)
[   17.787910][   T12]  netif_close_many_and_unlock (net/core/dev.c:12476)
[   17.788173][   T12]  unregister_netdevice_many_notify (net/core/dev.c:12539)
[   17.788391][   T12]  ? default_device_exit_batch (net/core/dev.c:13215)
[   17.788579][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   17.788746][   T12]  ? dev_ingress_queue_create (net/core/dev.c:12499)
[   17.789034][   T12]  ? rtnl_is_locked (net/core/rtnetlink.c:169)
[   17.789198][   T12]  ? unregister_netdevice_queue (net/core/dev.c:12442)
[   17.789405][   T12]  ? unregister_netdevice_many (net/core/dev.c:12441)
[   17.789676][   T12]  default_device_exit_batch (net/core/dev.c:13229)
[   17.789841][   T12]  ? unregister_netdev (net/core/dev.c:13204)
[   17.790022][   T12]  ops_undo_list (net/core/net_namespace.c:251)
[   17.790190][   T12]  ? rtnl_net_dumpid_one (net/core/net_namespace.c:223)
[   17.790449][   T12]  ? cleanup_net (./include/linux/list.h:191 net/core/net_namespace.c:693)
[   17.790624][   T12]  cleanup_net (net/core/net_namespace.c:698)
[   17.790789][   T12]  ? net_passive_dec (net/core/net_namespace.c:660)
[   17.790966][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   17.791228][   T12]  process_one_work (kernel/workqueue.c:3268)
[   17.791396][   T12]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   17.791570][   T12]  ? assign_work (kernel/workqueue.c:1206)
[   17.791741][   T12]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   17.792013][   T12]  ? rescuer_thread (kernel/workqueue.c:3373)
[   17.792178][   T12]  kthread (kernel/kthread.c:463)
[   17.792305][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   17.792467][   T12]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   17.792637][   T12]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   17.792803][   T12]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   17.792979][   T12]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   17.793144][   T12]  ret_from_fork (arch/x86/kernel/process.c:164)
[   17.793309][   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