======================================
| [  394.959339] ------------[ cut here ]------------
| [  394.959629] refcount_t: underflow; use-after-free.
| [  394.959911] WARNING: CPU: 2 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  394.960394] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[  394.961448] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  394.962072] Workqueue: netns cleanup_net
[  394.962304] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 394.962593] 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 2f 99 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 2f 99 	mov    $0xffffffff992f70a0,%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
[  394.963601] RSP: 0018:ffffa5970025bd78 EFLAGS: 00010286
[  394.963906] RAX: 0000000000000000 RBX: ffff8f36426ec000 RCX: 00000000ffffdfff
[  394.964292] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  394.964678] RBP: ffff8f36426ec5f8 R08: ffffffff99764508 R09: 00000000ffffdfff
[  394.965081] R10: ffffffff99684520 R11: ffffffff99734520 R12: ffff8f36426ec000
[  394.965472] R13: ffffa5970025be08 R14: ffff8f36426ecb60 R15: ffff8f3643950050
[  394.965872] FS:  0000000000000000(0000) GS:ffff8f367ed00000(0000) knlGS:0000000000000000
[  394.966325] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  394.966644] CR2: 00007fc399bdd0c8 CR3: 00000000026ce006 CR4: 00000000001706f0
[  394.967046] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  394.967450] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  394.967856] Call Trace:
[  394.968011]  <TASK>
[  394.968138] ? __warn (kernel/panic.c:677) 
[  394.968332] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  394.968599] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  394.968809] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  394.969025] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  394.969249] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  394.969495] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  394.969765] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  394.970034] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  394.970335] br_dev_delete (net/bridge/br_if.c:396) bridge
[  394.970587] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  394.970874] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  394.971088] ? process_one_work (kernel/workqueue.c:2606) 
[  394.971326] process_one_work (kernel/workqueue.c:2638) 
[  394.971544] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  394.971749] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  394.971985] kthread (kernel/kthread.c:388) 
[  394.972167] ? __pfx_kthread (kernel/kthread.c:341) 
[  394.972380] ret_from_fork (arch/x86/kernel/process.c:153) 
[  394.972598] ? __pfx_kthread (kernel/kthread.c:341) 
[  394.972818] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  394.975550] ------------[ cut here ]------------
| [  394.975797] sysfs group 'bridge' not found for kobject 'br2'
| [  394.976131] WARNING: CPU: 2 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  394.976579] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[  394.977719] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  394.978381] Workqueue: netns cleanup_net
[  394.978610] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 394.978909] 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 2f 99 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 2f 99 	mov    $0xffffffff992f0688,%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)
	...
[  394.979927] RSP: 0018:ffffa5970025bd70 EFLAGS: 00010286
[  394.980225] RAX: 0000000000000000 RBX: ffffffffc047dc60 RCX: 00000000ffffdfff
[  394.980619] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  394.981019] RBP: 0000000000000000 R08: ffffffff99764508 R09: 00000000ffffdfff
[  394.981396] R10: ffffffff99684520 R11: ffffffff99734520 R12: ffff8f36426ec5f8
[  394.981789] R13: ffffa5970025be08 R14: ffff8f36426ecb60 R15: ffff8f3643950050
[  394.982183] FS:  0000000000000000(0000) GS:ffff8f367ed00000(0000) knlGS:0000000000000000
[  394.982627] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  394.982954] CR2: 00007fc399bdd0c8 CR3: 00000000026ce006 CR4: 00000000001706f0
[  394.983380] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  394.983765] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  394.984149] Call Trace:
[  394.984286]  <TASK>
[  394.984424] ? __warn (kernel/panic.c:677) 
[  394.984610] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  394.984846] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  394.985056] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  394.985260] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  394.985480] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  394.985733] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  394.985971] br_dev_delete (net/bridge/br_if.c:396) bridge
[  394.986252] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  394.986542] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  394.986745] ? process_one_work (kernel/workqueue.c:2606) 
[  394.986972] process_one_work (kernel/workqueue.c:2638) 
[  394.987217] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  394.987437] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  394.987681] kthread (kernel/kthread.c:388) 
[  394.987857] ? __pfx_kthread (kernel/kthread.c:341) 
[  394.988069] ret_from_fork (arch/x86/kernel/process.c:153) 
[  394.988271] ? __pfx_kthread (kernel/kthread.c:341) 
[  394.988489] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  395.109189] ------------[ cut here ]------------
| [  395.109468] sysfs group 'bridge' not found for kobject 'br2'
| [  395.109808] WARNING: CPU: 1 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  395.110277] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[  395.111389] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  395.112019] Workqueue: netns cleanup_net
[  395.112248] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 395.112543] 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 2f 99 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 2f 99 	mov    $0xffffffff992f0688,%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)
	...
[  395.113562] RSP: 0018:ffffa5970025bd70 EFLAGS: 00010286
[  395.113860] RAX: 0000000000000000 RBX: ffffffffc047dc60 RCX: 00000000ffffdfff
[  395.114259] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  395.114658] RBP: 0000000000000000 R08: ffffffff99764508 R09: 00000000ffffdfff
[  395.115064] R10: ffffffff99684520 R11: ffffffff99734520 R12: ffff8f36426645f8
[  395.115452] R13: ffffa5970025be08 R14: ffff8f3642664b60 R15: ffffffff9ac13dd0
[  395.115830] FS:  0000000000000000(0000) GS:ffff8f367ec80000(0000) knlGS:0000000000000000
[  395.116262] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  395.116603] CR2: 00007fbd12e672a8 CR3: 000000000285c005 CR4: 00000000001706f0
[  395.116979] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  395.117477] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  395.117966] Call Trace:
[  395.118178]  <TASK>
[  395.118342] ? __warn (kernel/panic.c:677) 
[  395.118588] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  395.118927] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  395.119228] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  395.119516] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  395.119823] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  395.120175] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  395.120513] br_dev_delete (net/bridge/br_if.c:396) bridge
[  395.120896] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  395.121331] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  395.121624] ? process_one_work (kernel/workqueue.c:2606) 
[  395.121958] process_one_work (kernel/workqueue.c:2638) 
[  395.122293] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  395.122606] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  395.122946] kthread (kernel/kthread.c:388) 
[  395.123209] ? __pfx_kthread (kernel/kthread.c:341) 
[  395.123509] ret_from_fork (arch/x86/kernel/process.c:153) 
[  395.123796] ? __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