======================================
| [  863.518006] ------------[ cut here ]------------
| [  863.518267] refcount_t: underflow; use-after-free.
| [  863.518558] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  863.519029] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  863.520166] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  863.520762] Workqueue: netns cleanup_net
[  863.520987] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 863.521267] 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 2f b9 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 2f b9 	mov    $0xffffffffb92f70c8,%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
[  863.522250] RSP: 0018:ffffb42d40263d78 EFLAGS: 00010286
[  863.522534] RAX: 0000000000000000 RBX: ffff8e7c0190a000 RCX: 00000000ffffdfff
[  863.522935] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  863.523316] RBP: ffff8e7c0190a5f8 R08: ffffffffb9764508 R09: 00000000ffffdfff
[  863.523692] R10: ffffffffb9684520 R11: ffffffffb9734520 R12: ffff8e7c0190a000
[  863.524075] R13: ffffb42d40263e08 R14: ffff8e7c0190ab60 R15: ffff8e7c04e60050
[  863.524454] FS:  0000000000000000(0000) GS:ffff8e7c3ec80000(0000) knlGS:0000000000000000
[  863.524885] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  863.525188] CR2: 00007f3c0e45b1b4 CR3: 000000001f44c003 CR4: 00000000001706f0
[  863.525562] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  863.525941] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  863.526317] Call Trace:
[  863.526460]  <TASK>
[  863.526584] ? __warn (kernel/panic.c:677) 
[  863.526769] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  863.527027] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  863.527232] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  863.527426] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  863.527636] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  863.527874] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  863.528125] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  863.528380] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  863.528691] br_dev_delete (net/bridge/br_if.c:396) bridge
[  863.528954] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  863.529244] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  863.529442] ? process_one_work (kernel/workqueue.c:2606) 
[  863.529679] process_one_work (kernel/workqueue.c:2638) 
[  863.529920] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  863.530129] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  863.530386] kthread (kernel/kthread.c:388) 
[  863.530560] ? __pfx_kthread (kernel/kthread.c:341) 
[  863.530767] ret_from_fork (arch/x86/kernel/process.c:153) 
[  863.530981] ? __pfx_kthread (kernel/kthread.c:341) 
[  863.531194] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  863.534545] ------------[ cut here ]------------
| [  863.534939] sysfs group 'bridge' not found for kobject 'br2'
| [  863.535417] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  863.536079] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  863.537349] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  863.537950] Workqueue: netns cleanup_net
[  863.538185] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 863.538486] 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 2f b9 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 2f b9 	mov    $0xffffffffb92f06b0,%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)
	...
[  863.539757] RSP: 0018:ffffb42d40263d70 EFLAGS: 00010286
[  863.540182] RAX: 0000000000000000 RBX: ffffffffc0420c60 RCX: 00000000ffffdfff
[  863.540729] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  863.541298] RBP: 0000000000000000 R08: ffffffffb9764508 R09: 00000000ffffdfff
[  863.541859] R10: ffffffffb9684520 R11: ffffffffb9734520 R12: ffff8e7c0190a5f8
[  863.542399] R13: ffffb42d40263e08 R14: ffff8e7c0190ab60 R15: ffff8e7c04e60050
[  863.542977] FS:  0000000000000000(0000) GS:ffff8e7c3ec80000(0000) knlGS:0000000000000000
[  863.543605] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  863.544048] CR2: 00007f3c0e45b1b4 CR3: 000000001f44c003 CR4: 00000000001706f0
[  863.544601] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  863.545153] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  863.545724] Call Trace:
[  863.545931]  <TASK>
[  863.546113] ? __warn (kernel/panic.c:677) 
[  863.546382] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  863.546724] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  863.547023] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  863.547305] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  863.547617] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  863.547981] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  863.548328] br_dev_delete (net/bridge/br_if.c:396) bridge
[  863.548731] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  863.549178] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  863.549487] ? process_one_work (kernel/workqueue.c:2606) 
[  863.549843] process_one_work (kernel/workqueue.c:2638) 
[  863.550180] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  863.550446] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  863.550681] kthread (kernel/kthread.c:388) 
[  863.550881] ? __pfx_kthread (kernel/kthread.c:341) 
[  863.551085] ret_from_fork (arch/x86/kernel/process.c:153) 
[  863.551297] ? __pfx_kthread (kernel/kthread.c:341) 
[  863.551500] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  863.695119] ------------[ cut here ]------------
| [  863.695513] sysfs group 'bridge' not found for kobject 'br2'
| [  863.696007] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  863.696644] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[  863.698091] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  863.698700] Workqueue: netns cleanup_net
[  863.698945] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 863.699229] 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 2f b9 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 2f b9 	mov    $0xffffffffb92f06b0,%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)
	...
[  863.700246] RSP: 0018:ffffb42d40263d70 EFLAGS: 00010286
[  863.700542] RAX: 0000000000000000 RBX: ffffffffc0420c60 RCX: 00000000ffffdfff
[  863.700935] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  863.701326] RBP: 0000000000000000 R08: ffffffffb9764508 R09: 00000000ffffdfff
[  863.701698] R10: ffffffffb9684520 R11: ffffffffb9734520 R12: ffff8e7c021085f8
[  863.702094] R13: ffffb42d40263e08 R14: ffff8e7c02108b60 R15: ffffffffbac13dd0
[  863.702487] FS:  0000000000000000(0000) GS:ffff8e7c3ec80000(0000) knlGS:0000000000000000
[  863.702951] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  863.703268] CR2: 00007f953da51000 CR3: 000000001f44c005 CR4: 00000000001706f0
[  863.703659] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  863.704057] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  863.704453] Call Trace:
[  863.704594]  <TASK>
[  863.704737] ? __warn (kernel/panic.c:677) 
[  863.704941] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  863.705171] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  863.705374] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  863.705566] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  863.705795] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  863.706042] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  863.706282] br_dev_delete (net/bridge/br_if.c:396) bridge
[  863.706569] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  863.706899] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  863.707112] ? process_one_work (kernel/workqueue.c:2606) 
[  863.707353] process_one_work (kernel/workqueue.c:2638) 
[  863.707598] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  863.707814] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  863.708043] kthread (kernel/kthread.c:388) 
[  863.708219] ? __pfx_kthread (kernel/kthread.c:341) 
[  863.708424] ret_from_fork (arch/x86/kernel/process.c:153) 
[  863.708640] ? __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