======================================
| [   12.530352] ------------[ cut here ]------------
| [   12.530622] refcount_t: underflow; use-after-free.
| [   12.530900] WARNING: CPU: 0 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [   12.531366] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[   12.532311] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.532913] Workqueue: netns cleanup_net
[   12.533136] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 12.533424] 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 c8 70 8f 97 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 c8 70 8f 97 	mov    $0xffffffff978f70c8,%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
[   12.534401] RSP: 0018:ffffa3708025bd78 EFLAGS: 00010286
[   12.534685] RAX: 0000000000000000 RBX: ffff93dc42162000 RCX: 00000000ffffdfff
[   12.535069] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.535459] RBP: ffff93dc421625f8 R08: ffffffff97d64508 R09: 00000000ffffdfff
[   12.535852] R10: ffffffff97c84520 R11: ffffffff97d34520 R12: ffff93dc42162000
[   12.536242] R13: ffffa3708025be08 R14: ffff93dc42162b60 R15: ffff93dc42510050
[   12.536623] FS:  0000000000000000(0000) GS:ffff93dc7ec00000(0000) knlGS:0000000000000000
[   12.537051] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.537371] CR2: 00007ffd86137bb0 CR3: 000000000e44c001 CR4: 00000000001706f0
[   12.537744] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.538133] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.538516] Call Trace:
[   12.538655]  <TASK>
[   12.538776] ? __warn (kernel/panic.c:677) 
[   12.538964] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.539228] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.539434] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.539629] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.539860] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.540093] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.540362] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.540613] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[   12.540906] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.541169] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.541460] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.541662] ? process_one_work (kernel/workqueue.c:2606) 
[   12.541888] process_one_work (kernel/workqueue.c:2638) 
[   12.542110] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.542340] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.542574] kthread (kernel/kthread.c:388) 
[   12.542755] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.542962] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.543174] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.543382] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   12.546013] ------------[ cut here ]------------
| [   12.546272] sysfs group 'bridge' not found for kobject 'br2'
| [   12.546592] WARNING: CPU: 0 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   12.547023] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[   12.548011] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.548620] Workqueue: netns cleanup_net
[   12.548871] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 12.549206] 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 b0 06 8f 97 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 b0 06 8f 97 	mov    $0xffffffff978f06b0,%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)
	...
[   12.550189] RSP: 0018:ffffa3708025bd70 EFLAGS: 00010286
[   12.550470] RAX: 0000000000000000 RBX: ffffffffc04dac60 RCX: 00000000ffffdfff
[   12.550859] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.551241] RBP: 0000000000000000 R08: ffffffff97d64508 R09: 00000000ffffdfff
[   12.551618] R10: ffffffff97c84520 R11: ffffffff97d34520 R12: ffff93dc421625f8
[   12.552008] R13: ffffa3708025be08 R14: ffff93dc42162b60 R15: ffff93dc42510050
[   12.552402] FS:  0000000000000000(0000) GS:ffff93dc7ec00000(0000) knlGS:0000000000000000
[   12.552853] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.553296] CR2: 00007ffd86137bb0 CR3: 000000000e44c001 CR4: 00000000001706f0
[   12.553832] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.554397] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.554945] Call Trace:
[   12.555163]  <TASK>
[   12.555342] ? __warn (kernel/panic.c:677) 
[   12.555609] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.555940] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.556255] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.556541] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.556847] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.557204] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.557546] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.557927] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.558367] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.558672] ? process_one_work (kernel/workqueue.c:2606) 
[   12.559005] process_one_work (kernel/workqueue.c:2638) 
[   12.559353] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.559662] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.560013] kthread (kernel/kthread.c:388) 
[   12.560287] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.560595] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.560886] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.561204] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   12.664444] ------------[ cut here ]------------
| [   12.664716] sysfs group 'bridge' not found for kobject 'br2'
| [   12.665042] WARNING: CPU: 0 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   12.665493] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[   12.666502] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.667117] Workqueue: netns cleanup_net
[   12.667349] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 12.667610] 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 b0 06 8f 97 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 b0 06 8f 97 	mov    $0xffffffff978f06b0,%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)
	...
[   12.668592] RSP: 0018:ffffa3708025bd70 EFLAGS: 00010286
[   12.668874] RAX: 0000000000000000 RBX: ffffffffc04dac60 RCX: 00000000ffffdfff
[   12.669255] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.669628] RBP: 0000000000000000 R08: ffffffff97d64508 R09: 00000000ffffdfff
[   12.670030] R10: ffffffff97c84520 R11: ffffffff97d34520 R12: ffff93dc421605f8
[   12.670416] R13: ffffa3708025be08 R14: ffff93dc42160b60 R15: ffffffff99213dd0
[   12.670795] FS:  0000000000000000(0000) GS:ffff93dc7ec00000(0000) knlGS:0000000000000000
[   12.671228] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.671536] CR2: 0000559792a913c8 CR3: 000000000e44c001 CR4: 00000000001706f0
[   12.671921] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.672332] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.672716] Call Trace:
[   12.672857]  <TASK>
[   12.672981] ? __warn (kernel/panic.c:677) 
[   12.673167] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.673399] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.673603] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.673797] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.674036] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.674279] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.674509] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.674768] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.675059] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.675269] ? process_one_work (kernel/workqueue.c:2606) 
[   12.675499] process_one_work (kernel/workqueue.c:2638) 
[   12.675721] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.675930] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.676173] kthread (kernel/kthread.c:388) 
[   12.676350] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.676556] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.676758] ? __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