======================================
| [  100.978218] ------------[ cut here ]------------
| [  100.978483] refcount_t: underflow; use-after-free.
| [  100.978764] WARNING: CPU: 3 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  100.979225] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel ip6_gre ip6_tunnel tunnel6 gre act_pedit act_gact cls_flower sch_ingress bridge stp llc 8021q vrf veth
[  100.980424] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  100.981034] Workqueue: netns cleanup_net
[  100.981262] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 100.981550] 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 84 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 84 	mov    $0xffffffff848f70a0,%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
[  100.982534] RSP: 0018:ffffbfbec0063d78 EFLAGS: 00010286
[  100.982834] RAX: 0000000000000000 RBX: ffff9e52c21ca000 RCX: 00000000ffffdfff
[  100.983236] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  100.983620] RBP: ffff9e52c21ca5f8 R08: ffffffff84d64508 R09: 00000000ffffdfff
[  100.984003] R10: ffffffff84c84520 R11: ffffffff84d34520 R12: ffff9e52c21ca000
[  100.984394] R13: ffffbfbec0063e08 R14: ffff9e52c21cab60 R15: ffff9e52c5f68050
[  100.984778] FS:  0000000000000000(0000) GS:ffff9e52fed80000(0000) knlGS:0000000000000000
[  100.985220] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  100.985562] CR2: 00007f01e7a880c8 CR3: 0000000001cb4006 CR4: 00000000001706f0
[  100.985949] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  100.986338] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  100.986718] Call Trace:
[  100.986855]  <TASK>
[  100.986977] ? __warn (kernel/panic.c:677) 
[  100.987169] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  100.987422] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  100.987632] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  100.987832] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  100.988047] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  100.988292] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  100.988547] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  100.988800] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  100.989099] br_dev_delete (net/bridge/br_if.c:396) bridge
[  100.989353] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  100.989641] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  100.989845] ? process_one_work (kernel/workqueue.c:2606) 
[  100.990079] process_one_work (kernel/workqueue.c:2638) 
[  100.990304] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  100.990510] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  100.990748] kthread (kernel/kthread.c:388) 
[  100.990925] ? __pfx_kthread (kernel/kthread.c:341) 
[  100.991140] ret_from_fork (arch/x86/kernel/process.c:153) 
[  100.991345] ? __pfx_kthread (kernel/kthread.c:341) 
[  100.991553] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  100.994187] ------------[ cut here ]------------
| [  100.994439] sysfs group 'bridge' not found for kobject 'br2'
| [  100.994760] WARNING: CPU: 3 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  100.995206] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel ip6_gre ip6_tunnel tunnel6 gre act_pedit act_gact cls_flower sch_ingress bridge stp llc 8021q vrf veth
[  100.996464] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  100.997074] Workqueue: netns cleanup_net
[  100.997291] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 100.997552] 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 84 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 84 	mov    $0xffffffff848f0688,%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)
	...
[  100.998556] RSP: 0018:ffffbfbec0063d70 EFLAGS: 00010286
[  100.998842] RAX: 0000000000000000 RBX: ffffffffc0508c60 RCX: 00000000ffffdfff
[  100.999232] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  100.999626] RBP: 0000000000000000 R08: ffffffff84d64508 R09: 00000000ffffdfff
[  101.000005] R10: ffffffff84c84520 R11: ffffffff84d34520 R12: ffff9e52c21ca5f8
[  101.000390] R13: ffffbfbec0063e08 R14: ffff9e52c21cab60 R15: ffff9e52c5f68050
[  101.000773] FS:  0000000000000000(0000) GS:ffff9e52fed80000(0000) knlGS:0000000000000000
[  101.001208] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  101.001515] CR2: 00007f01e7a880c8 CR3: 0000000001cb4006 CR4: 00000000001706f0
[  101.001893] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  101.002277] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  101.002657] Call Trace:
[  101.002806]  <TASK>
[  101.002927] ? __warn (kernel/panic.c:677) 
[  101.003113] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  101.003342] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  101.003550] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  101.003748] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  101.003962] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  101.004204] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  101.004436] br_dev_delete (net/bridge/br_if.c:396) bridge
[  101.004696] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  101.004990] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  101.005195] ? process_one_work (kernel/workqueue.c:2606) 
[  101.005426] process_one_work (kernel/workqueue.c:2638) 
[  101.005650] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  101.005860] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  101.006099] kthread (kernel/kthread.c:388) 
[  101.006276] ? __pfx_kthread (kernel/kthread.c:341) 
[  101.006484] ret_from_fork (arch/x86/kernel/process.c:153) 
[  101.006681] ? __pfx_kthread (kernel/kthread.c:341) 
[  101.006888] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  101.119223] ------------[ cut here ]------------
| [  101.119496] sysfs group 'bridge' not found for kobject 'br2'
| [  101.119825] WARNING: CPU: 3 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  101.120283] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel ip6_gre ip6_tunnel tunnel6 gre act_pedit act_gact cls_flower sch_ingress bridge stp llc 8021q vrf veth
[  101.121568] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  101.122190] Workqueue: netns cleanup_net
[  101.122412] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 101.122675] 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 84 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 84 	mov    $0xffffffff848f0688,%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)
	...
[  101.123677] RSP: 0018:ffffbfbec0063d70 EFLAGS: 00010286
[  101.123961] RAX: 0000000000000000 RBX: ffffffffc0508c60 RCX: 00000000ffffdfff
[  101.124348] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  101.124730] RBP: 0000000000000000 R08: ffffffff84d64508 R09: 00000000ffffdfff
[  101.125119] R10: ffffffff84c84520 R11: ffffffff84d34520 R12: ffff9e52c21c85f8
[  101.125501] R13: ffffbfbec0063e08 R14: ffff9e52c21c8b60 R15: ffffffff86213dd0
[  101.125882] FS:  0000000000000000(0000) GS:ffff9e52fed80000(0000) knlGS:0000000000000000
[  101.126317] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  101.126633] CR2: 00007f7455b7d270 CR3: 0000000005da4005 CR4: 00000000001706f0
[  101.127022] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  101.127416] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  101.127797] Call Trace:
[  101.127939]  <TASK>
[  101.128068] ? __warn (kernel/panic.c:677) 
[  101.128253] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  101.128488] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  101.128699] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  101.128898] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  101.129116] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  101.129354] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  101.129587] br_dev_delete (net/bridge/br_if.c:396) bridge
[  101.129852] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  101.130152] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  101.130355] ? process_one_work (kernel/workqueue.c:2606) 
[  101.130588] process_one_work (kernel/workqueue.c:2638) 
[  101.130817] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  101.131027] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  101.131270] kthread (kernel/kthread.c:388) 
[  101.131454] ? __pfx_kthread (kernel/kthread.c:341) 
[  101.131664] ret_from_fork (arch/x86/kernel/process.c:153) 
[  101.131866] ? __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