======================================
| [  226.859258] ------------[ cut here ]------------
| [  226.859532] refcount_t: underflow; use-after-free.
| [  226.859812] WARNING: CPU: 0 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  226.860293] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred cls_flower 8021q ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress bridge stp llc vrf veth
[  226.861657] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  226.862296] Workqueue: netns cleanup_net
[  226.862535] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 226.862836] 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 af 94 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 af 94 	mov    $0xffffffff94af70a0,%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
[  226.863885] RSP: 0018:ffffb65980063d78 EFLAGS: 00010286
[  226.864197] RAX: 0000000000000000 RBX: ffff8f05024d8000 RCX: 00000000ffffdfff
[  226.864604] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  226.865016] RBP: ffff8f05024d85f8 R08: ffffffff94f64508 R09: 00000000ffffdfff
[  226.865427] R10: ffffffff94e84520 R11: ffffffff94f34520 R12: ffff8f05024d8000
[  226.865845] R13: ffffb65980063e08 R14: ffff8f05024d8b60 R15: ffff8f0503b68050
[  226.866258] FS:  0000000000000000(0000) GS:ffff8f053ec00000(0000) knlGS:0000000000000000
[  226.866713] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  226.867024] CR2: 000055c6fb6dcc50 CR3: 000000000269c001 CR4: 00000000001706f0
[  226.867400] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  226.867783] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  226.868174] Call Trace:
[  226.868315]  <TASK>
[  226.868440] ? __warn (kernel/panic.c:677) 
[  226.868622] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  226.868904] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  226.869122] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  226.869328] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  226.869541] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  226.869772] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  226.870046] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  226.870315] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  226.870623] br_dev_delete (net/bridge/br_if.c:396) bridge
[  226.870908] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  226.871215] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  226.871437] ? process_one_work (kernel/workqueue.c:2606) 
[  226.871679] process_one_work (kernel/workqueue.c:2638) 
[  226.871925] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  226.872145] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  226.872397] kthread (kernel/kthread.c:388) 
[  226.872579] ? __pfx_kthread (kernel/kthread.c:341) 
[  226.872796] ret_from_fork (arch/x86/kernel/process.c:153) 
[  226.873024] ? __pfx_kthread (kernel/kthread.c:341) 
[  226.873245] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  226.875937] ------------[ cut here ]------------
| [  226.876204] sysfs group 'bridge' not found for kobject 'br2'
| [  226.876538] WARNING: CPU: 0 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  226.876990] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred cls_flower 8021q ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress bridge stp llc vrf veth
[  226.878538] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  226.879168] Workqueue: netns cleanup_net
[  226.879392] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 226.879676] 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 af 94 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 af 94 	mov    $0xffffffff94af0688,%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)
	...
[  226.880653] RSP: 0018:ffffb65980063d70 EFLAGS: 00010286
[  226.880950] RAX: 0000000000000000 RBX: ffffffffc0505c60 RCX: 00000000ffffdfff
[  226.881331] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  226.881718] RBP: 0000000000000000 R08: ffffffff94f64508 R09: 00000000ffffdfff
[  226.882110] R10: ffffffff94e84520 R11: ffffffff94f34520 R12: ffff8f05024d85f8
[  226.882501] R13: ffffb65980063e08 R14: ffff8f05024d8b60 R15: ffff8f0503b68050
[  226.882877] FS:  0000000000000000(0000) GS:ffff8f053ec00000(0000) knlGS:0000000000000000
[  226.883329] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  226.883639] CR2: 000055c6fb6dcc50 CR3: 000000000269c001 CR4: 00000000001706f0
[  226.884035] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  226.884426] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  226.884815] Call Trace:
[  226.884968]  <TASK>
[  226.885093] ? __warn (kernel/panic.c:677) 
[  226.885290] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  226.885524] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  226.885736] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  226.885948] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  226.886165] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  226.886407] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  226.886636] br_dev_delete (net/bridge/br_if.c:396) bridge
[  226.886918] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  226.887211] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  226.887428] ? process_one_work (kernel/workqueue.c:2606) 
[  226.887659] process_one_work (kernel/workqueue.c:2638) 
[  226.887905] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  226.888119] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  226.888366] kthread (kernel/kthread.c:388) 
[  226.888549] ? __pfx_kthread (kernel/kthread.c:341) 
[  226.888755] ret_from_fork (arch/x86/kernel/process.c:153) 
[  226.888976] ? __pfx_kthread (kernel/kthread.c:341) 
[  226.889182] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  227.000100] ------------[ cut here ]------------
| [  227.000373] sysfs group 'bridge' not found for kobject 'br2'
| [  227.000755] WARNING: CPU: 1 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  227.001250] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred cls_flower 8021q ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress bridge stp llc vrf veth
[  227.002624] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  227.003252] Workqueue: netns cleanup_net
[  227.003484] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 227.003749] 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 af 94 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 af 94 	mov    $0xffffffff94af0688,%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)
	...
[  227.004749] RSP: 0018:ffffb65980063d70 EFLAGS: 00010286
[  227.005045] RAX: 0000000000000000 RBX: ffffffffc0505c60 RCX: 00000000ffffdfff
[  227.005463] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  227.005845] RBP: 0000000000000000 R08: ffffffff94f64508 R09: 00000000ffffdfff
[  227.006234] R10: ffffffff94e84520 R11: ffffffff94f34520 R12: ffff8f05023ce5f8
[  227.006623] R13: ffffb65980063e08 R14: ffff8f05023ceb60 R15: ffffffff96413dd0
[  227.007018] FS:  0000000000000000(0000) GS:ffff8f053ec80000(0000) knlGS:0000000000000000
[  227.007452] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  227.007761] CR2: 000055c6fb6dcc50 CR3: 000000000269c001 CR4: 00000000001706f0
[  227.008153] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  227.008541] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  227.008934] Call Trace:
[  227.009078]  <TASK>
[  227.009236] ? __warn (kernel/panic.c:677) 
[  227.009426] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  227.009657] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  227.009864] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  227.010069] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  227.010283] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  227.010521] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  227.010764] br_dev_delete (net/bridge/br_if.c:396) bridge
[  227.011034] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  227.011329] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  227.011534] ? process_one_work (kernel/workqueue.c:2606) 
[  227.011769] process_one_work (kernel/workqueue.c:2638) 
[  227.012002] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  227.012217] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  227.012451] kthread (kernel/kthread.c:388) 
[  227.012632] ? __pfx_kthread (kernel/kthread.c:341) 
[  227.012845] ret_from_fork (arch/x86/kernel/process.c:153) 
[  227.013056] ? __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
sysfs_remove_group:br_dev_delete:br_net_exit_batch_rtnl:cleanup_net