======================================
| [  512.579140] ------------[ cut here ]------------
| [  512.579531] refcount_t: underflow; use-after-free.
| [  512.579961] WARNING: CPU: 0 PID: 69 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  512.580628] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel sch_ingress bridge stp llc 8021q vrf veth
[  512.582117] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  512.583011] Workqueue: netns cleanup_net
[  512.583340] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 512.583766] 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 4f 9b 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 4f 9b 	mov    $0xffffffff9b4f70c8,%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
[  512.585221] RSP: 0018:ffff98228026bd78 EFLAGS: 00010286
[  512.585649] RAX: 0000000000000000 RBX: ffff89b50274c000 RCX: 00000000ffffdfff
[  512.586227] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  512.586792] RBP: ffff89b50274c5f8 R08: ffffffff9b964508 R09: 00000000ffffdfff
[  512.587366] R10: ffffffff9b884520 R11: ffffffff9b934520 R12: ffff89b50274c000
[  512.587938] R13: ffff98228026be08 R14: ffff89b50274cb60 R15: ffff89b5026d8050
[  512.588514] FS:  0000000000000000(0000) GS:ffff89b53ec00000(0000) knlGS:0000000000000000
[  512.589171] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  512.589641] CR2: 00007fd62cf9d50e CR3: 000000003404c002 CR4: 00000000001706f0
[  512.590225] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  512.590808] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  512.591392] Call Trace:
[  512.591613]  <TASK>
[  512.591800] ? __warn (kernel/panic.c:677) 
[  512.592090] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  512.592477] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  512.592792] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  512.593095] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  512.593418] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  512.593776] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  512.594165] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  512.594545] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  512.594996] br_dev_delete (net/bridge/br_if.c:396) bridge
[  512.595383] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  512.595822] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  512.596156] ? process_one_work (kernel/workqueue.c:2606) 
[  512.596505] process_one_work (kernel/workqueue.c:2638) 
[  512.596856] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  512.597174] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  512.597526] kthread (kernel/kthread.c:388) 
[  512.597795] ? __pfx_kthread (kernel/kthread.c:341) 
[  512.598117] ret_from_fork (arch/x86/kernel/process.c:153) 
[  512.598417] ? __pfx_kthread (kernel/kthread.c:341) 
[  512.598732] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  512.601932] ------------[ cut here ]------------
| [  512.602186] sysfs group 'bridge' not found for kobject 'br2'
| [  512.602512] WARNING: CPU: 0 PID: 69 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  512.602956] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel sch_ingress bridge stp llc 8021q vrf veth
[  512.604032] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  512.604642] Workqueue: netns cleanup_net
[  512.604868] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 512.605131] 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 4f 9b 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 4f 9b 	mov    $0xffffffff9b4f06b0,%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)
	...
[  512.606125] RSP: 0018:ffff98228026bd70 EFLAGS: 00010286
[  512.606410] RAX: 0000000000000000 RBX: ffffffffc0359c60 RCX: 00000000ffffdfff
[  512.606798] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  512.607190] RBP: 0000000000000000 R08: ffffffff9b964508 R09: 00000000ffffdfff
[  512.607577] R10: ffffffff9b884520 R11: ffffffff9b934520 R12: ffff89b50274c5f8
[  512.607967] R13: ffff98228026be08 R14: ffff89b50274cb60 R15: ffff89b5026d8050
[  512.608352] FS:  0000000000000000(0000) GS:ffff89b53ec00000(0000) knlGS:0000000000000000
[  512.608783] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  512.609103] CR2: 00007fd62cf9d50e CR3: 000000003404c002 CR4: 00000000001706f0
[  512.609485] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  512.609872] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  512.610258] Call Trace:
[  512.610409]  <TASK>
[  512.610535] ? __warn (kernel/panic.c:677) 
[  512.610722] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  512.610959] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  512.611169] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  512.611365] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  512.611576] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  512.611812] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  512.612050] br_dev_delete (net/bridge/br_if.c:396) bridge
[  512.612318] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  512.612615] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  512.612820] ? process_one_work (kernel/workqueue.c:2606) 
[  512.613064] process_one_work (kernel/workqueue.c:2638) 
[  512.613286] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  512.613494] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  512.613733] kthread (kernel/kthread.c:388) 
[  512.613919] ? __pfx_kthread (kernel/kthread.c:341) 
[  512.614131] ret_from_fork (arch/x86/kernel/process.c:153) 
[  512.614336] ? __pfx_kthread (kernel/kthread.c:341) 
[  512.614544] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  512.719017] ------------[ cut here ]------------
| [  512.719289] sysfs group 'bridge' not found for kobject 'br2'
| [  512.719618] WARNING: CPU: 0 PID: 69 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  512.720096] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel sch_ingress bridge stp llc 8021q vrf veth
[  512.721211] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  512.721839] Workqueue: netns cleanup_net
[  512.722073] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 512.722347] 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 4f 9b 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 4f 9b 	mov    $0xffffffff9b4f06b0,%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)
	...
[  512.723349] RSP: 0018:ffff98228026bd70 EFLAGS: 00010286
[  512.723642] RAX: 0000000000000000 RBX: ffffffffc0359c60 RCX: 00000000ffffdfff
[  512.724050] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  512.724445] RBP: 0000000000000000 R08: ffffffff9b964508 R09: 00000000ffffdfff
[  512.724838] R10: ffffffff9b884520 R11: ffffffff9b934520 R12: ffff89b501d5c5f8
[  512.725220] R13: ffff98228026be08 R14: ffff89b501d5cb60 R15: ffffffff9ce13dd0
[  512.725609] FS:  0000000000000000(0000) GS:ffff89b53ec00000(0000) knlGS:0000000000000000
[  512.726056] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  512.726372] CR2: 00005584a8d20dec CR3: 0000000003668005 CR4: 00000000001706f0
[  512.726756] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  512.727146] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  512.727547] Call Trace:
[  512.727693]  <TASK>
[  512.727819] ? __warn (kernel/panic.c:677) 
[  512.728020] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  512.728252] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  512.728472] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  512.728684] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  512.728906] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  512.729154] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  512.729395] br_dev_delete (net/bridge/br_if.c:396) bridge
[  512.729673] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  512.729978] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  512.730184] ? process_one_work (kernel/workqueue.c:2606) 
[  512.730431] process_one_work (kernel/workqueue.c:2638) 
[  512.730662] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  512.730877] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  512.731125] kthread (kernel/kthread.c:388) 
[  512.731304] ? __pfx_kthread (kernel/kthread.c:341) 
[  512.731511] ret_from_fork (arch/x86/kernel/process.c:153) 
[  512.731723] ? __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