======================================
| [  830.048834] ------------[ cut here ]------------
| [  830.049109] refcount_t: underflow; use-after-free.
| [  830.049404] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  830.049864] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[  830.050935] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  830.051550] Workqueue: netns cleanup_net
[  830.051781] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 830.052065] 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 cf 90 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 cf 90 	mov    $0xffffffff90cf70a0,%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
[  830.053057] RSP: 0018:ffffb0d000263d78 EFLAGS: 00010286
[  830.053353] RAX: 0000000000000000 RBX: ffff90be463f8000 RCX: 00000000ffffdfff
[  830.053748] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  830.054131] RBP: ffff90be463f85f8 R08: ffffffff91164508 R09: 00000000ffffdfff
[  830.054513] R10: ffffffff91084520 R11: ffffffff91134520 R12: ffff90be463f8000
[  830.054907] R13: ffffb0d000263e08 R14: ffff90be463f8b60 R15: ffff90be42738050
[  830.055294] FS:  0000000000000000(0000) GS:ffff90be7ec80000(0000) knlGS:0000000000000000
[  830.055744] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  830.056056] CR2: 000055e1f2c9c408 CR3: 0000000002994005 CR4: 00000000001706f0
[  830.056449] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  830.056839] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  830.057228] Call Trace:
[  830.057373]  <TASK>
[  830.057499] ? __warn (kernel/panic.c:677) 
[  830.057693] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  830.057952] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  830.058160] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  830.058358] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  830.058569] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  830.058816] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  830.059073] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  830.059331] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  830.059637] br_dev_delete (net/bridge/br_if.c:396) bridge
[  830.059897] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  830.060266] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  830.060530] ? process_one_work (kernel/workqueue.c:2606) 
[  830.060855] process_one_work (kernel/workqueue.c:2638) 
[  830.061088] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  830.061391] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  830.061679] kthread (kernel/kthread.c:388) 
[  830.061903] ? __pfx_kthread (kernel/kthread.c:341) 
[  830.062197] ret_from_fork (arch/x86/kernel/process.c:153) 
[  830.062471] ? __pfx_kthread (kernel/kthread.c:341) 
[  830.062768] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  830.066297] ------------[ cut here ]------------
| [  830.066654] sysfs group 'bridge' not found for kobject 'br2'
| [  830.067084] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  830.067684] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[  830.068807] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  830.069512] Workqueue: netns cleanup_net
[  830.069743] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 830.070088] 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 cf 90 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 cf 90 	mov    $0xffffffff90cf0688,%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)
	...
[  830.071283] RSP: 0018:ffffb0d000263d70 EFLAGS: 00010286
[  830.071653] RAX: 0000000000000000 RBX: ffffffffc035dc60 RCX: 00000000ffffdfff
[  830.072164] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  830.072693] RBP: 0000000000000000 R08: ffffffff91164508 R09: 00000000ffffdfff
[  830.073206] R10: ffffffff91084520 R11: ffffffff91134520 R12: ffff90be463f85f8
[  830.073730] R13: ffffb0d000263e08 R14: ffff90be463f8b60 R15: ffff90be42738050
[  830.074238] FS:  0000000000000000(0000) GS:ffff90be7ec80000(0000) knlGS:0000000000000000
[  830.074828] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  830.075231] CR2: 000055e1f2c9c408 CR3: 0000000002994005 CR4: 00000000001706f0
[  830.075748] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  830.076248] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  830.076763] Call Trace:
[  830.076959]  <TASK>
[  830.077109] ? __warn (kernel/panic.c:677) 
[  830.077359] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  830.077676] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  830.077933] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  830.078201] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  830.078468] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  830.078798] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  830.079057] br_dev_delete (net/bridge/br_if.c:396) bridge
[  830.079318] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  830.079633] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  830.079841] ? process_one_work (kernel/workqueue.c:2606) 
[  830.080084] process_one_work (kernel/workqueue.c:2638) 
[  830.080307] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  830.080517] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  830.080759] kthread (kernel/kthread.c:388) 
[  830.080939] ? __pfx_kthread (kernel/kthread.c:341) 
[  830.081151] ret_from_fork (arch/x86/kernel/process.c:153) 
[  830.081360] ? __pfx_kthread (kernel/kthread.c:341) 
[  830.081566] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  830.194799] ------------[ cut here ]------------
| [  830.195075] sysfs group 'bridge' not found for kobject 'br2'
| [  830.195409] WARNING: CPU: 3 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  830.195870] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[  830.197034] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  830.197662] Workqueue: netns cleanup_net
[  830.197910] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 830.198179] 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 cf 90 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 cf 90 	mov    $0xffffffff90cf0688,%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)
	...
[  830.199173] RSP: 0018:ffffb0d000263d70 EFLAGS: 00010286
[  830.199459] RAX: 0000000000000000 RBX: ffffffffc035dc60 RCX: 00000000ffffdfff
[  830.199852] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  830.200239] RBP: 0000000000000000 R08: ffffffff91164508 R09: 00000000ffffdfff
[  830.200634] R10: ffffffff91084520 R11: ffffffff91134520 R12: ffff90be463fc5f8
[  830.201020] R13: ffffb0d000263e08 R14: ffff90be463fcb60 R15: ffffffff92613dd0
[  830.201404] FS:  0000000000000000(0000) GS:ffff90be7ed80000(0000) knlGS:0000000000000000
[  830.201881] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  830.202203] CR2: 00007f533c35b000 CR3: 000000003524c002 CR4: 00000000001706f0
[  830.202620] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  830.203004] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  830.203387] Call Trace:
[  830.203535]  <TASK>
[  830.203667] ? __warn (kernel/panic.c:677) 
[  830.203858] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  830.204092] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  830.204309] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  830.204511] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  830.204734] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  830.204977] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  830.205216] br_dev_delete (net/bridge/br_if.c:396) bridge
[  830.205487] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  830.205818] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  830.206027] ? process_one_work (kernel/workqueue.c:2606) 
[  830.206271] process_one_work (kernel/workqueue.c:2638) 
[  830.206498] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  830.206714] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  830.206956] kthread (kernel/kthread.c:388) 
[  830.207137] ? __pfx_kthread (kernel/kthread.c:341) 
[  830.207352] ret_from_fork (arch/x86/kernel/process.c:153) 
[  830.207557] ? __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