======================================
| [  829.587408] ------------[ cut here ]------------
| [  829.587822] refcount_t: underflow; use-after-free.
| [  829.588276] WARNING: CPU: 3 PID: 10 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  829.588961] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred cls_matchall sch_red dummy act_gact cls_flower sch_ingress ip_gre gre em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  829.591142] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  829.592099] Workqueue: netns cleanup_net
[  829.592440] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 829.592884] 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 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 a0 70 af 97 	mov    $0xffffffff97af70a0,%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
[  829.594424] RSP: 0018:ffffb840c005bd78 EFLAGS: 00010286
[  829.594837] RAX: 0000000000000000 RBX: ffff947941f0a000 RCX: 00000000ffffdfff
[  829.595346] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  829.595783] RBP: ffff947941f0a5f8 R08: ffffffff97f64508 R09: 00000000ffffdfff
[  829.596192] R10: ffffffff97e84520 R11: ffffffff97f34520 R12: ffff947941f0a000
[  829.596594] R13: ffffb840c005be08 R14: ffff947941f0ab60 R15: ffff947945620050
[  829.596988] FS:  0000000000000000(0000) GS:ffff94797ed80000(0000) knlGS:0000000000000000
[  829.597427] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  829.597744] CR2: 00007efd9f4e3270 CR3: 000000002844c004 CR4: 00000000001706f0
[  829.598141] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  829.598540] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  829.598935] Call Trace:
[  829.599083]  <TASK>
[  829.599219] ? __warn (kernel/panic.c:677) 
[  829.599411] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  829.599673] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  829.599883] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  829.600087] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  829.600308] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  829.600544] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  829.600802] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  829.601068] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  829.601373] br_dev_delete (net/bridge/br_if.c:396) bridge
[  829.601634] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  829.601933] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  829.602145] ? process_one_work (kernel/workqueue.c:2606) 
[  829.602386] process_one_work (kernel/workqueue.c:2638) 
[  829.602623] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  829.602834] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  829.603079] kthread (kernel/kthread.c:388) 
[  829.603271] ? __pfx_kthread (kernel/kthread.c:341) 
[  829.603484] ret_from_fork (arch/x86/kernel/process.c:153) 
[  829.603687] ? __pfx_kthread (kernel/kthread.c:341) 
[  829.603898] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  829.607049] ------------[ cut here ]------------
| [  829.607415] sysfs group 'bridge' not found for kobject 'br2'
| [  829.607882] WARNING: CPU: 3 PID: 10 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  829.608531] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred cls_matchall sch_red dummy act_gact cls_flower sch_ingress ip_gre gre em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  829.610671] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  829.611566] Workqueue: netns cleanup_net
[  829.611891] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 829.612286] 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 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 88 06 af 97 	mov    $0xffffffff97af0688,%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)
	...
[  829.613738] RSP: 0018:ffffb840c005bd70 EFLAGS: 00010286
[  829.614167] RAX: 0000000000000000 RBX: ffffffffc0562c60 RCX: 00000000ffffdfff
[  829.614745] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  829.615321] RBP: 0000000000000000 R08: ffffffff97f64508 R09: 00000000ffffdfff
[  829.615879] R10: ffffffff97e84520 R11: ffffffff97f34520 R12: ffff947941f0a5f8
[  829.616453] R13: ffffb840c005be08 R14: ffff947941f0ab60 R15: ffff947945620050
[  829.616850] FS:  0000000000000000(0000) GS:ffff94797ed80000(0000) knlGS:0000000000000000
[  829.617300] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  829.617614] CR2: 00007efd9f4e3270 CR3: 000000002844c004 CR4: 00000000001706f0
[  829.618008] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  829.618396] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  829.618807] Call Trace:
[  829.618957]  <TASK>
[  829.619105] ? __warn (kernel/panic.c:677) 
[  829.619296] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  829.619542] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  829.619760] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  829.619972] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  829.620213] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  829.620464] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  829.620704] br_dev_delete (net/bridge/br_if.c:396) bridge
[  829.620994] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  829.621301] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  829.621510] ? process_one_work (kernel/workqueue.c:2606) 
[  829.621743] process_one_work (kernel/workqueue.c:2638) 
[  829.621967] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  829.622181] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  829.622464] kthread (kernel/kthread.c:388) 
[  829.622653] ? __pfx_kthread (kernel/kthread.c:341) 
[  829.622862] ret_from_fork (arch/x86/kernel/process.c:153) 
[  829.623085] ? __pfx_kthread (kernel/kthread.c:341) 
[  829.623318] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  829.750174] ------------[ cut here ]------------
| [  829.750461] sysfs group 'bridge' not found for kobject 'br2'
| [  829.750814] WARNING: CPU: 0 PID: 10 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  829.751305] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred cls_matchall sch_red dummy act_gact cls_flower sch_ingress ip_gre gre em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  829.752864] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  829.753483] Workqueue: netns cleanup_net
[  829.753721] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 829.753998] 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 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 88 06 af 97 	mov    $0xffffffff97af0688,%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)
	...
[  829.755025] RSP: 0018:ffffb840c005bd70 EFLAGS: 00010286
[  829.755335] RAX: 0000000000000000 RBX: ffffffffc0562c60 RCX: 00000000ffffdfff
[  829.755716] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  829.756142] RBP: 0000000000000000 R08: ffffffff97f64508 R09: 00000000ffffdfff
[  829.756561] R10: ffffffff97e84520 R11: ffffffff97f34520 R12: ffff947942afa5f8
[  829.756970] R13: ffffb840c005be08 R14: ffff947942afab60 R15: ffffffff99413dd0
[  829.757391] FS:  0000000000000000(0000) GS:ffff94797ec00000(0000) knlGS:0000000000000000
[  829.757860] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  829.758200] CR2: 0000559d43005670 CR3: 00000000029d4001 CR4: 00000000001706f0
[  829.758613] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  829.759022] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  829.759434] Call Trace:
[  829.759587]  <TASK>
[  829.759719] ? __warn (kernel/panic.c:677) 
[  829.759910] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  829.760170] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  829.760394] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  829.760610] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  829.760840] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  829.761104] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  829.761358] br_dev_delete (net/bridge/br_if.c:396) bridge
[  829.761636] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  829.761950] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  829.762173] ? process_one_work (kernel/workqueue.c:2606) 
[  829.762423] process_one_work (kernel/workqueue.c:2638) 
[  829.762658] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  829.762888] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  829.763157] kthread (kernel/kthread.c:388) 
[  829.763337] ? __pfx_kthread (kernel/kthread.c:341) 
[  829.763546] ret_from_fork (arch/x86/kernel/process.c:153) 
[  829.763756] ? __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