======================================
| [   25.590148] ------------[ cut here ]------------
| [   25.590427] refcount_t: underflow; use-after-free.
| [   25.590708] WARNING: CPU: 2 PID: 10 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [   25.591185] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel 8021q sch_ingress bridge stp llc vrf veth
[   25.592112] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   25.592723] Workqueue: netns cleanup_net
[   25.592953] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 25.593244] 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 cf b3 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 cf b3 	mov    $0xffffffffb3cf70a0,%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
[   25.594232] RSP: 0018:ffffb2250005bd78 EFLAGS: 00010286
[   25.594525] RAX: 0000000000000000 RBX: ffff9bf44250a000 RCX: 00000000ffffdfff
[   25.594908] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   25.595310] RBP: ffff9bf44250a5f8 R08: ffffffffb4164508 R09: 00000000ffffdfff
[   25.595697] R10: ffffffffb4084520 R11: ffffffffb4134520 R12: ffff9bf44250a000
[   25.596087] R13: ffffb2250005be08 R14: ffff9bf44250ab60 R15: ffff9bf445bc0050
[   25.596492] FS:  0000000000000000(0000) GS:ffff9bf47ed00000(0000) knlGS:0000000000000000
[   25.596925] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   25.597250] CR2: 00007f61012f11b4 CR3: 000000002a24c004 CR4: 00000000001706f0
[   25.597644] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   25.598035] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   25.598422] Call Trace:
[   25.598568]  <TASK>
[   25.598693] ? __warn (kernel/panic.c:677) 
[   25.598880] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   25.599144] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   25.599352] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   25.599548] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   25.599763] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   25.600003] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   25.600270] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   25.600532] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[   25.600833] br_dev_delete (net/bridge/br_if.c:396) bridge
[   25.601099] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   25.601405] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   25.601608] ? process_one_work (kernel/workqueue.c:2606) 
[   25.601845] process_one_work (kernel/workqueue.c:2638) 
[   25.602077] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   25.602291] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   25.602527] kthread (kernel/kthread.c:388) 
[   25.602707] ? __pfx_kthread (kernel/kthread.c:341) 
[   25.602919] ret_from_fork (arch/x86/kernel/process.c:153) 
[   25.603125] ? __pfx_kthread (kernel/kthread.c:341) 
[   25.603336] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   25.606397] ------------[ cut here ]------------
| [   25.606769] sysfs group 'bridge' not found for kobject 'br2'
| [   25.607251] WARNING: CPU: 2 PID: 10 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   25.607889] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel 8021q sch_ingress bridge stp llc vrf veth
[   25.609346] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   25.610246] Workqueue: netns cleanup_net
[   25.610572] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 25.610970] 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 cf b3 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 cf b3 	mov    $0xffffffffb3cf0688,%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)
	...
[   25.612426] RSP: 0018:ffffb2250005bd70 EFLAGS: 00010286
[   25.612847] RAX: 0000000000000000 RBX: ffffffffc0493c60 RCX: 00000000ffffdfff
[   25.613419] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   25.613993] RBP: 0000000000000000 R08: ffffffffb4164508 R09: 00000000ffffdfff
[   25.614565] R10: ffffffffb4084520 R11: ffffffffb4134520 R12: ffff9bf44250a5f8
[   25.615134] R13: ffffb2250005be08 R14: ffff9bf44250ab60 R15: ffff9bf445bc0050
[   25.615605] FS:  0000000000000000(0000) GS:ffff9bf47ed00000(0000) knlGS:0000000000000000
[   25.616056] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   25.616370] CR2: 00007f61012f11b4 CR3: 000000002a24c004 CR4: 00000000001706f0
[   25.616756] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   25.617154] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   25.617575] Call Trace:
[   25.617718]  <TASK>
[   25.617844] ? __warn (kernel/panic.c:677) 
[   25.618038] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   25.618277] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   25.618490] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   25.618689] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   25.618909] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   25.619154] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   25.619392] br_dev_delete (net/bridge/br_if.c:396) bridge
[   25.619664] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   25.619966] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   25.620174] ? process_one_work (kernel/workqueue.c:2606) 
[   25.620409] process_one_work (kernel/workqueue.c:2638) 
[   25.620636] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   25.620852] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   25.621094] kthread (kernel/kthread.c:388) 
[   25.621273] ? __pfx_kthread (kernel/kthread.c:341) 
[   25.621490] ret_from_fork (arch/x86/kernel/process.c:153) 
[   25.621714] ? __pfx_kthread (kernel/kthread.c:341) 
[   25.621925] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   25.707206] ------------[ cut here ]------------
| [   25.707599] sysfs group 'bridge' not found for kobject 'br2'
| [   25.708093] WARNING: CPU: 2 PID: 10 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   25.708752] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel 8021q sch_ingress bridge stp llc vrf veth
[   25.710248] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   25.711177] Workqueue: netns cleanup_net
[   25.711503] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 25.711903] 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 cf b3 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 cf b3 	mov    $0xffffffffb3cf0688,%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)
	...
[   25.713392] RSP: 0018:ffffb2250005bd70 EFLAGS: 00010286
[   25.713818] RAX: 0000000000000000 RBX: ffffffffc0493c60 RCX: 00000000ffffdfff
[   25.714395] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   25.714984] RBP: 0000000000000000 R08: ffffffffb4164508 R09: 00000000ffffdfff
[   25.715564] R10: ffffffffb4084520 R11: ffffffffb4134520 R12: ffff9bf4426245f8
[   25.716150] R13: ffffb2250005be08 R14: ffff9bf442624b60 R15: ffffffffb5613dd0
[   25.716723] FS:  0000000000000000(0000) GS:ffff9bf47ed00000(0000) knlGS:0000000000000000
[   25.717390] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   25.717854] CR2: 0000562c25594dec CR3: 00000000025c2005 CR4: 00000000001706f0
[   25.718436] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   25.719023] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   25.719605] Call Trace:
[   25.719815]  <TASK>
[   25.720016] ? __warn (kernel/panic.c:677) 
[   25.720292] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   25.720638] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   25.720957] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   25.721251] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   25.721568] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   25.721920] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   25.722278] br_dev_delete (net/bridge/br_if.c:396) bridge
[   25.722675] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   25.723131] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   25.723440] ? process_one_work (kernel/workqueue.c:2606) 
[   25.723784] process_one_work (kernel/workqueue.c:2638) 
[   25.724133] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   25.724449] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   25.724803] kthread (kernel/kthread.c:388) 
[   25.725079] ? __pfx_kthread (kernel/kthread.c:341) 
[   25.725406] ret_from_fork (arch/x86/kernel/process.c:153) 
[   25.725702] ? __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