======================================
| [  858.665237] ------------[ cut here ]------------
| [  858.665502] refcount_t: underflow; use-after-free.
| [  858.665797] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  858.666267] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  858.667429] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  858.668043] Workqueue: netns cleanup_net
[  858.668264] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 858.668550] 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 2f 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 2f a7 	mov    $0xffffffffa72f70a0,%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
[  858.669543] RSP: 0018:ffffb2da00263d78 EFLAGS: 00010286
[  858.669830] RAX: 0000000000000000 RBX: ffff9ebd425a0000 RCX: 00000000ffffdfff
[  858.670223] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  858.670614] RBP: ffff9ebd425a05f8 R08: ffffffffa7764508 R09: 00000000ffffdfff
[  858.670997] R10: ffffffffa7684520 R11: ffffffffa7734520 R12: ffff9ebd425a0000
[  858.671376] R13: ffffb2da00263e08 R14: ffff9ebd425a0b60 R15: ffff9ebd45b68050
[  858.671755] FS:  0000000000000000(0000) GS:ffff9ebd7ec80000(0000) knlGS:0000000000000000
[  858.672199] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  858.672516] CR2: 00000000004e1f88 CR3: 0000000005bf2003 CR4: 00000000001706f0
[  858.672908] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  858.673289] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  858.673667] Call Trace:
[  858.673807]  <TASK>
[  858.673937] ? __warn (kernel/panic.c:677) 
[  858.674129] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  858.674383] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  858.674592] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  858.674791] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  858.675018] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  858.675257] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  858.675515] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  858.675769] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  858.676075] br_dev_delete (net/bridge/br_if.c:396) bridge
[  858.676329] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  858.676620] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  858.676824] ? process_one_work (kernel/workqueue.c:2606) 
[  858.677063] process_one_work (kernel/workqueue.c:2638) 
[  858.677284] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  858.677491] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  858.677729] kthread (kernel/kthread.c:388) 
[  858.677913] ? __pfx_kthread (kernel/kthread.c:341) 
[  858.678122] ret_from_fork (arch/x86/kernel/process.c:153) 
[  858.678327] ? __pfx_kthread (kernel/kthread.c:341) 
[  858.678535] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  858.681278] ------------[ cut here ]------------
| [  858.681527] sysfs group 'bridge' not found for kobject 'br2'
| [  858.681855] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  858.682291] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  858.683504] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  858.684123] Workqueue: netns cleanup_net
[  858.684346] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 858.684607] 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 2f 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 2f a7 	mov    $0xffffffffa72f0688,%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)
	...
[  858.685603] RSP: 0018:ffffb2da00263d70 EFLAGS: 00010286
[  858.685889] RAX: 0000000000000000 RBX: ffffffffc03aac60 RCX: 00000000ffffdfff
[  858.686278] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  858.686665] RBP: 0000000000000000 R08: ffffffffa7764508 R09: 00000000ffffdfff
[  858.687054] R10: ffffffffa7684520 R11: ffffffffa7734520 R12: ffff9ebd425a05f8
[  858.687441] R13: ffffb2da00263e08 R14: ffff9ebd425a0b60 R15: ffff9ebd45b68050
[  858.687830] FS:  0000000000000000(0000) GS:ffff9ebd7ec80000(0000) knlGS:0000000000000000
[  858.688271] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  858.688579] CR2: 00000000004e1f88 CR3: 0000000005bf2003 CR4: 00000000001706f0
[  858.688967] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  858.689355] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  858.689741] Call Trace:
[  858.689881]  <TASK>
[  858.690011] ? __warn (kernel/panic.c:677) 
[  858.690193] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  858.690422] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  858.690649] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  858.690849] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  858.691071] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  858.691311] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  858.691546] br_dev_delete (net/bridge/br_if.c:396) bridge
[  858.691810] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  858.692112] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  858.692317] ? process_one_work (kernel/workqueue.c:2606) 
[  858.692551] process_one_work (kernel/workqueue.c:2638) 
[  858.692779] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  858.692998] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  858.693234] kthread (kernel/kthread.c:388) 
[  858.693415] ? __pfx_kthread (kernel/kthread.c:341) 
[  858.693628] ret_from_fork (arch/x86/kernel/process.c:153) 
[  858.693835] ? __pfx_kthread (kernel/kthread.c:341) 
[  858.694066] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  858.818088] ------------[ cut here ]------------
| [  858.818352] sysfs group 'bridge' not found for kobject 'br2'
| [  858.818682] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  858.819142] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  858.820391] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  858.821012] Workqueue: netns cleanup_net
[  858.821233] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 858.821496] 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 2f 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 2f a7 	mov    $0xffffffffa72f0688,%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)
	...
[  858.822490] RSP: 0018:ffffb2da00263d70 EFLAGS: 00010286
[  858.822778] RAX: 0000000000000000 RBX: ffffffffc03aac60 RCX: 00000000ffffdfff
[  858.823170] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  858.823560] RBP: 0000000000000000 R08: ffffffffa7764508 R09: 00000000ffffdfff
[  858.823953] R10: ffffffffa7684520 R11: ffffffffa7734520 R12: ffff9ebd423705f8
[  858.824336] R13: ffffb2da00263e08 R14: ffff9ebd42370b60 R15: ffffffffa8c13dd0
[  858.824723] FS:  0000000000000000(0000) GS:ffff9ebd7ec80000(0000) knlGS:0000000000000000
[  858.825167] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  858.825479] CR2: 00007f6cd5f751b4 CR3: 0000000008c4c001 CR4: 00000000001706f0
[  858.825863] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  858.826253] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  858.826640] Call Trace:
[  858.826788]  <TASK>
[  858.826920] ? __warn (kernel/panic.c:677) 
[  858.827111] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  858.827342] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  858.827551] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  858.827748] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  858.827972] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  858.828210] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  858.828444] br_dev_delete (net/bridge/br_if.c:396) bridge
[  858.828715] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  858.829014] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  858.829222] ? process_one_work (kernel/workqueue.c:2606) 
[  858.829454] process_one_work (kernel/workqueue.c:2638) 
[  858.829678] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  858.829887] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  858.830132] kthread (kernel/kthread.c:388) 
[  858.830309] ? __pfx_kthread (kernel/kthread.c:341) 
[  858.830526] ret_from_fork (arch/x86/kernel/process.c:153) 
[  858.830730] ? __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