======================================
| [  450.344519] ------------[ cut here ]------------
| [  450.344909] refcount_t: underflow; use-after-free.
| [  450.345334] WARNING: CPU: 2 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  450.345983] Modules linked in: macvlan vxlan ip6_udp_tunnel udp_tunnel act_vlan cls_matchall ip_gre bridge stp llc act_mirred act_police act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  450.348096] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  450.348993] Workqueue: netns cleanup_net
[  450.349319] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 450.349734] Code: 0b 90 90 c3 cc cc cc cc 80 3d a1 b9 66 01 00 0f 85 75 ff ff ff c6 05 94 b9 66 01 01 90 48 c7 c7 a0 70 8f 82 e8 71 92 b4 ff 90 <0f> 0b 90 90 c3 cc cc cc cc 80 3d 74 b9 66 01 00 0f 85 4a ff ff ff
All code
========
   0:	0b 90 90 c3 cc cc    	or     -0x33333c70(%rax),%edx
   6:	cc                   	int3
   7:	cc                   	int3
   8:	80 3d a1 b9 66 01 00 	cmpb   $0x0,0x166b9a1(%rip)        # 0x166b9b0
   f:	0f 85 75 ff ff ff    	jne    0xffffffffffffff8a
  15:	c6 05 94 b9 66 01 01 	movb   $0x1,0x166b994(%rip)        # 0x166b9b0
  1c:	90                   	nop
  1d:	48 c7 c7 a0 70 8f 82 	mov    $0xffffffff828f70a0,%rdi
  24:	e8 71 92 b4 ff       	call   0xffffffffffb4929a
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	c3                   	ret
  2f:	cc                   	int3
  30:	cc                   	int3
  31:	cc                   	int3
  32:	cc                   	int3
  33:	80 3d 74 b9 66 01 00 	cmpb   $0x0,0x166b974(%rip)        # 0x166b9ae
  3a:	0f 85 4a ff ff ff    	jne    0xffffffffffffff8a

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	c3                   	ret
   5:	cc                   	int3
   6:	cc                   	int3
   7:	cc                   	int3
   8:	cc                   	int3
   9:	80 3d 74 b9 66 01 00 	cmpb   $0x0,0x166b974(%rip)        # 0x166b984
  10:	0f 85 4a ff ff ff    	jne    0xffffffffffffff60
[  450.351171] RSP: 0018:ffffc0780025bd78 EFLAGS: 00010286
[  450.351591] RAX: 0000000000000000 RBX: ffff9dddc25a4000 RCX: 00000000ffffdfff
[  450.352165] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  450.352728] RBP: ffff9dddc25a45f8 R08: ffffffff82d64508 R09: 00000000ffffdfff
[  450.353292] R10: ffffffff82c84520 R11: ffffffff82d34520 R12: ffff9dddc25a4000
[  450.353849] R13: ffffc0780025be08 R14: ffff9dddc25a4b60 R15: ffffffff84213dd0
[  450.354417] FS:  0000000000000000(0000) GS:ffff9dddfed00000(0000) knlGS:0000000000000000
[  450.355053] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  450.355510] CR2: 00007f295a6642a8 CR3: 000000002e64c002 CR4: 00000000001706f0
[  450.356081] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  450.356645] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  450.357228] Call Trace:
[  450.357434]  <TASK>
[  450.357616] ? __warn (kernel/panic.c:677) 
[  450.357890] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  450.358268] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  450.358576] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  450.358867] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  450.359187] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  450.359536] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  450.359909] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  450.360288] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  450.360712] br_dev_delete (net/bridge/br_if.c:396) bridge
[  450.361100] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  450.361529] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  450.361830] ? process_one_work (kernel/workqueue.c:2606) 
[  450.362175] process_one_work (kernel/workqueue.c:2638) 
[  450.362503] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  450.362813] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  450.363168] kthread (kernel/kthread.c:388) 
[  450.363429] ? __pfx_kthread (kernel/kthread.c:341) 
[  450.363736] ret_from_fork (arch/x86/kernel/process.c:153) 
[  450.364040] ? __pfx_kthread (kernel/kthread.c:341) 
[  450.364343] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  450.368198] ------------[ cut here ]------------
| [  450.368567] sysfs group 'bridge' not found for kobject 'br1'
| [  450.369049] WARNING: CPU: 2 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  450.369688] Modules linked in: macvlan vxlan ip6_udp_tunnel udp_tunnel act_vlan cls_matchall ip_gre bridge stp llc act_mirred act_police act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  450.371859] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  450.372752] Workqueue: netns cleanup_net
[  450.373083] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 450.373465] Code: 48 89 ef 5d 41 5c e9 0a ae ff ff 48 89 ef e8 a2 9b ff ff eb d1 90 49 8b 14 24 48 8b 33 48 c7 c7 88 06 8f 82 e8 fc b0 c5 ff 90 <0f> 0b 90 90 5b 5d 41 5c c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00
All code
========
   0:	48 89 ef             	mov    %rbp,%rdi
   3:	5d                   	pop    %rbp
   4:	41 5c                	pop    %r12
   6:	e9 0a ae ff ff       	jmp    0xffffffffffffae15
   b:	48 89 ef             	mov    %rbp,%rdi
   e:	e8 a2 9b ff ff       	call   0xffffffffffff9bb5
  13:	eb d1                	jmp    0xffffffffffffffe6
  15:	90                   	nop
  16:	49 8b 14 24          	mov    (%r12),%rdx
  1a:	48 8b 33             	mov    (%rbx),%rsi
  1d:	48 c7 c7 88 06 8f 82 	mov    $0xffffffff828f0688,%rdi
  24:	e8 fc b0 c5 ff       	call   0xffffffffffc5b125
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	5b                   	pop    %rbx
  2f:	5d                   	pop    %rbp
  30:	41 5c                	pop    %r12
  32:	c3                   	ret
  33:	cc                   	int3
  34:	cc                   	int3
  35:	cc                   	int3
  36:	cc                   	int3
  37:	66                   	data16
  38:	66                   	data16
  39:	2e                   	cs
  3a:	0f                   	.byte 0xf
  3b:	1f                   	(bad)
  3c:	84 00                	test   %al,(%rax)
	...

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	5b                   	pop    %rbx
   5:	5d                   	pop    %rbp
   6:	41 5c                	pop    %r12
   8:	c3                   	ret
   9:	cc                   	int3
   a:	cc                   	int3
   b:	cc                   	int3
   c:	cc                   	int3
   d:	66                   	data16
   e:	66                   	data16
   f:	2e                   	cs
  10:	0f                   	.byte 0xf
  11:	1f                   	(bad)
  12:	84 00                	test   %al,(%rax)
	...
[  450.374900] RSP: 0018:ffffc0780025bd70 EFLAGS: 00010286
[  450.375327] RAX: 0000000000000000 RBX: ffffffffc05ccc60 RCX: 00000000ffffdfff
[  450.375883] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  450.376446] RBP: 0000000000000000 R08: ffffffff82d64508 R09: 00000000ffffdfff
[  450.377022] R10: ffffffff82c84520 R11: ffffffff82d34520 R12: ffff9dddc25a45f8
[  450.377576] R13: ffffc0780025be08 R14: ffff9dddc25a4b60 R15: ffffffff84213dd0
[  450.378142] FS:  0000000000000000(0000) GS:ffff9dddfed00000(0000) knlGS:0000000000000000
[  450.378769] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  450.379231] CR2: 00007f295a6642a8 CR3: 000000002e64c002 CR4: 00000000001706f0
[  450.379789] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  450.380352] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  450.380907] Call Trace:
[  450.381120]  <TASK>
[  450.381301] ? __warn (kernel/panic.c:677) 
[  450.381571] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  450.381906] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  450.382220] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  450.382507] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  450.382813] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  450.383167] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  450.383505] br_dev_delete (net/bridge/br_if.c:396) bridge
[  450.383884] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  450.384317] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  450.384619] ? process_one_work (kernel/workqueue.c:2606) 
[  450.384953] process_one_work (kernel/workqueue.c:2638) 
[  450.385291] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  450.385596] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  450.385944] kthread (kernel/kthread.c:388) 
[  450.386216] ? __pfx_kthread (kernel/kthread.c:341) 
[  450.386528] ret_from_fork (arch/x86/kernel/process.c:153) 
[  450.386823] ? __pfx_kthread (kernel/kthread.c:341) 


Finger prints:
refcount_warn_saturate:br_sysfs_delbr:br_dev_delete:br_net_exit_batch_rtnl
sysfs_remove_group:br_dev_delete:br_net_exit_batch_rtnl:cleanup_net