======================================
| [ 1327.573250] ------------[ cut here ]------------
| [ 1327.573617] refcount_t: underflow; use-after-free.
| [ 1327.573913] WARNING: CPU: 3 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [ 1327.574398] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_pedit cls_matchall act_mirred dummy bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[ 1327.575702] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1327.576350] Workqueue: netns cleanup_net
[ 1327.576594] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1327.576888] 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 8f 9a 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 8f 9a 	mov    $0xffffffff9a8f70a0,%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
[ 1327.577937] RSP: 0018:ffffacbd00063d78 EFLAGS: 00010286
[ 1327.578242] RAX: 0000000000000000 RBX: ffff9ee542850000 RCX: 00000000ffffdfff
[ 1327.578654] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1327.579052] RBP: ffff9ee5428505f8 R08: ffffffff9ad64508 R09: 00000000ffffdfff
[ 1327.579444] R10: ffffffff9ac84520 R11: ffffffff9ad34520 R12: ffff9ee542850000
[ 1327.579863] R13: ffffacbd00063e08 R14: ffff9ee542850b60 R15: ffff9ee542790050
[ 1327.580264] FS:  0000000000000000(0000) GS:ffff9ee57ed80000(0000) knlGS:0000000000000000
[ 1327.580724] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1327.581054] CR2: 00007fff69037028 CR3: 000000000390c005 CR4: 00000000001706f0
[ 1327.581459] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1327.581852] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1327.582261] Call Trace:
[ 1327.582411]  <TASK>
[ 1327.582541] ? __warn (kernel/panic.c:677) 
[ 1327.582732] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1327.583007] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1327.583225] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1327.583428] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1327.583646] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1327.583888] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1327.584158] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1327.584420] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[ 1327.584736] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1327.585009] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1327.585308] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1327.585518] ? process_one_work (kernel/workqueue.c:2606) 
[ 1327.585756] process_one_work (kernel/workqueue.c:2638) 
[ 1327.585996] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1327.586214] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1327.586454] kthread (kernel/kthread.c:388) 
[ 1327.586639] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1327.586857] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1327.587072] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1327.587286] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1327.589991] ------------[ cut here ]------------
| [ 1327.590255] sysfs group 'bridge' not found for kobject 'br2'
| [ 1327.590587] WARNING: CPU: 3 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1327.591042] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_pedit cls_matchall act_mirred dummy bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[ 1327.592379] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1327.593087] Workqueue: netns cleanup_net
[ 1327.593440] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1327.593855] 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 8f 9a 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 8f 9a 	mov    $0xffffffff9a8f0688,%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)
	...
[ 1327.595412] RSP: 0018:ffffacbd00063d70 EFLAGS: 00010286
[ 1327.595861] RAX: 0000000000000000 RBX: ffffffffc0589c60 RCX: 00000000ffffdfff
[ 1327.596473] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1327.597046] RBP: 0000000000000000 R08: ffffffff9ad64508 R09: 00000000ffffdfff
[ 1327.597441] R10: ffffffff9ac84520 R11: ffffffff9ad34520 R12: ffff9ee5428505f8
[ 1327.597844] R13: ffffacbd00063e08 R14: ffff9ee542850b60 R15: ffff9ee542790050
[ 1327.598255] FS:  0000000000000000(0000) GS:ffff9ee57ed80000(0000) knlGS:0000000000000000
[ 1327.598700] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1327.599030] CR2: 00007fff69037028 CR3: 000000000390c005 CR4: 00000000001706f0
[ 1327.599429] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1327.599822] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1327.600219] Call Trace:
[ 1327.600362]  <TASK>
[ 1327.600488] ? __warn (kernel/panic.c:677) 
[ 1327.600693] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1327.600932] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1327.601152] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1327.601356] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1327.601573] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1327.601816] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1327.602062] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1327.602331] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1327.602631] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1327.602837] ? process_one_work (kernel/workqueue.c:2606) 
[ 1327.603083] process_one_work (kernel/workqueue.c:2638) 
[ 1327.603317] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1327.603531] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1327.603772] kthread (kernel/kthread.c:388) 
[ 1327.603970] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1327.604188] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1327.604392] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1327.604625] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1327.720294] ------------[ cut here ]------------
| [ 1327.720569] sysfs group 'bridge' not found for kobject 'br2'
| [ 1327.720905] WARNING: CPU: 0 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1327.721365] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_pedit cls_matchall act_mirred dummy bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[ 1327.722698] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1327.723320] Workqueue: netns cleanup_net
[ 1327.723547] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1327.723810] 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 8f 9a 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 8f 9a 	mov    $0xffffffff9a8f0688,%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)
	...
[ 1327.724802] RSP: 0018:ffffacbd00063d70 EFLAGS: 00010286
[ 1327.725094] RAX: 0000000000000000 RBX: ffffffffc0589c60 RCX: 00000000ffffdfff
[ 1327.725513] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1327.725932] RBP: 0000000000000000 R08: ffffffff9ad64508 R09: 00000000ffffdfff
[ 1327.726352] R10: ffffffff9ac84520 R11: ffffffff9ad34520 R12: ffff9ee5428525f8
[ 1327.726763] R13: ffffacbd00063e08 R14: ffff9ee542852b60 R15: ffffffff9c213dd0
[ 1327.727155] FS:  0000000000000000(0000) GS:ffff9ee57ec00000(0000) knlGS:0000000000000000
[ 1327.727602] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1327.727935] CR2: 00007fa12abbb30d CR3: 000000000277e006 CR4: 00000000001706f0
[ 1327.728331] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1327.728722] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1327.729113] Call Trace:
[ 1327.729254]  <TASK>
[ 1327.729379] ? __warn (kernel/panic.c:677) 
[ 1327.729564] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1327.729808] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1327.730033] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1327.730234] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1327.730449] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1327.730688] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1327.730927] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1327.731204] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1327.731499] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1327.731711] ? process_one_work (kernel/workqueue.c:2606) 
[ 1327.731944] process_one_work (kernel/workqueue.c:2638) 
[ 1327.732182] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1327.732395] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1327.732633] kthread (kernel/kthread.c:388) 
[ 1327.732819] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1327.733045] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1327.733256] ? __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