======================================
| [   12.280028] ------------[ cut here ]------------
| [   12.280379] refcount_t: underflow; use-after-free.
| [   12.280660] WARNING: CPU: 1 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [   12.281149] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc sch_ingress vrf veth
[   12.282108] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.282799] Workqueue: netns cleanup_net
[   12.283093] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 12.283392] 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 a7 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 a7 	mov    $0xffffffffa7af70a0,%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
[   12.284622] RSP: 0018:ffffc29140063d78 EFLAGS: 00010286
[   12.285029] RAX: 0000000000000000 RBX: ffffa0ddc2f60000 RCX: 00000000ffffdfff
[   12.285545] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.286057] RBP: ffffa0ddc2f605f8 R08: ffffffffa7f64508 R09: 00000000ffffdfff
[   12.286566] R10: ffffffffa7e84520 R11: ffffffffa7f34520 R12: ffffa0ddc2f60000
[   12.287083] R13: ffffc29140063e08 R14: ffffa0ddc2f60b60 R15: ffffa0ddc2790050
[   12.287571] FS:  0000000000000000(0000) GS:ffffa0ddfec80000(0000) knlGS:0000000000000000
[   12.288153] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.288561] CR2: 0000000000483760 CR3: 0000000002cd0001 CR4: 00000000001706f0
[   12.289083] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.289596] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.290099] Call Trace:
[   12.290274]  <TASK>
[   12.290443] ? __warn (kernel/panic.c:677) 
[   12.290699] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.290967] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.291199] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.291398] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.291624] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.291872] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.292126] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.292379] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[   12.292680] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.292943] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.293242] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.293447] ? process_one_work (kernel/workqueue.c:2606) 
[   12.293679] process_one_work (kernel/workqueue.c:2638) 
[   12.293914] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.294122] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.294357] kthread (kernel/kthread.c:388) 
[   12.294541] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.294750] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.294959] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.295170] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   12.297795] ------------[ cut here ]------------
| [   12.298047] sysfs group 'bridge' not found for kobject 'br2'
| [   12.298368] WARNING: CPU: 1 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   12.298812] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc sch_ingress vrf veth
[   12.299762] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.300363] Workqueue: netns cleanup_net
[   12.300579] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 12.300845] 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 a7 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 a7 	mov    $0xffffffffa7af0688,%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)
	...
[   12.301836] RSP: 0018:ffffc29140063d70 EFLAGS: 00010286
[   12.302138] RAX: 0000000000000000 RBX: ffffffffc064fc60 RCX: 00000000ffffdfff
[   12.302628] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.303066] RBP: 0000000000000000 R08: ffffffffa7f64508 R09: 00000000ffffdfff
[   12.303540] R10: ffffffffa7e84520 R11: ffffffffa7f34520 R12: ffffa0ddc2f605f8
[   12.304047] R13: ffffc29140063e08 R14: ffffa0ddc2f60b60 R15: ffffa0ddc2790050
[   12.304556] FS:  0000000000000000(0000) GS:ffffa0ddfec80000(0000) knlGS:0000000000000000
[   12.305143] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.305553] CR2: 0000000000483760 CR3: 0000000002cd0001 CR4: 00000000001706f0
[   12.306068] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.306584] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.307110] Call Trace:
[   12.307298]  <TASK>
[   12.307443] ? __warn (kernel/panic.c:677) 
[   12.307683] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.308003] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.308262] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.308524] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.308799] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.309120] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.309373] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.309641] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.309938] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.310155] ? process_one_work (kernel/workqueue.c:2606) 
[   12.310443] process_one_work (kernel/workqueue.c:2638) 
[   12.310667] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.310887] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.311175] kthread (kernel/kthread.c:388) 
[   12.311395] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.311683] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.311893] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.312125] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   12.410908] ------------[ cut here ]------------
| [   12.411187] sysfs group 'bridge' not found for kobject 'br2'
| [   12.411520] WARNING: CPU: 0 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   12.411974] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc sch_ingress vrf veth
[   12.412928] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.413523] Workqueue: netns cleanup_net
[   12.413747] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 12.414021] 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 a7 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 a7 	mov    $0xffffffffa7af0688,%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)
	...
[   12.414991] RSP: 0018:ffffc29140063d70 EFLAGS: 00010286
[   12.415273] RAX: 0000000000000000 RBX: ffffffffc064fc60 RCX: 00000000ffffdfff
[   12.415649] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.416039] RBP: 0000000000000000 R08: ffffffffa7f64508 R09: 00000000ffffdfff
[   12.416422] R10: ffffffffa7e84520 R11: ffffffffa7f34520 R12: ffffa0ddc50245f8
[   12.416801] R13: ffffc29140063e08 R14: ffffa0ddc5024b60 R15: ffffffffa9413dd0
[   12.417178] FS:  0000000000000000(0000) GS:ffffa0ddfec00000(0000) knlGS:0000000000000000
[   12.417607] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.417922] CR2: 00000000004e1f80 CR3: 000000000264a001 CR4: 00000000001706f0
[   12.418301] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.418675] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.419056] Call Trace:
[   12.419196]  <TASK>
[   12.419317] ? __warn (kernel/panic.c:677) 
[   12.419496] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.419728] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.419951] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.420146] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.420361] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.420595] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.420843] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.421121] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.421410] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.421614] ? process_one_work (kernel/workqueue.c:2606) 
[   12.421848] process_one_work (kernel/workqueue.c:2638) 
[   12.422070] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.422276] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.422512] kthread (kernel/kthread.c:388) 
[   12.422686] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.422896] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.423099] ? __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