======================================
| [  170.824809] ------------[ cut here ]------------
| [  170.825084] refcount_t: underflow; use-after-free.
| [  170.825360] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  170.825846] Modules linked in: macvlan vxlan ip6_udp_tunnel udp_tunnel xfrm_user 8021q act_mirred cls_flower bridge stp llc ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress vrf veth
[  170.827239] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  170.828054] Workqueue: netns cleanup_net
[  170.828380] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 170.828803] 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 88 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 88 	mov    $0xffffffff88cf70a0,%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
[  170.829794] RSP: 0018:ffffac8200263d78 EFLAGS: 00010286
[  170.830083] RAX: 0000000000000000 RBX: ffffa01f427a6000 RCX: 00000000ffffdfff
[  170.830473] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  170.830855] RBP: ffffa01f427a65f8 R08: ffffffff89164508 R09: 00000000ffffdfff
[  170.831231] R10: ffffffff89084520 R11: ffffffff89134520 R12: ffffa01f427a6000
[  170.831615] R13: ffffac8200263e08 R14: ffffa01f427a6b60 R15: ffffffff8a613dd0
[  170.832002] FS:  0000000000000000(0000) GS:ffffa01f7ec80000(0000) knlGS:0000000000000000
[  170.832437] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  170.832905] CR2: 000000000044a3a0 CR3: 00000000029d4002 CR4: 00000000001706f0
[  170.833352] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  170.833738] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  170.834121] Call Trace:
[  170.834261]  <TASK>
[  170.834383] ? __warn (kernel/panic.c:677) 
[  170.834579] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  170.834840] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  170.835046] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  170.835239] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  170.835457] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  170.835899] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  170.836155] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  170.836409] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  170.836713] br_dev_delete (net/bridge/br_if.c:396) bridge
[  170.836976] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  170.837266] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  170.837482] ? process_one_work (kernel/workqueue.c:2606) 
[  170.837708] process_one_work (kernel/workqueue.c:2638) 
[  170.837939] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  170.838147] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  170.838385] kthread (kernel/kthread.c:388) 
[  170.838569] ? __pfx_kthread (kernel/kthread.c:341) 
[  170.838779] ret_from_fork (arch/x86/kernel/process.c:153) 
[  170.838981] ? __pfx_kthread (kernel/kthread.c:341) 
[  170.839185] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  170.841899] ------------[ cut here ]------------
| [  170.842148] sysfs group 'bridge' not found for kobject 'br1'
| [  170.842480] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  170.842917] Modules linked in: macvlan vxlan ip6_udp_tunnel udp_tunnel xfrm_user 8021q act_mirred cls_flower bridge stp llc ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress vrf veth
[  170.844364] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  170.845045] Workqueue: netns cleanup_net
[  170.845263] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 170.845530] 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 88 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 88 	mov    $0xffffffff88cf0688,%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)
	...
[  170.846519] RSP: 0018:ffffac8200263d70 EFLAGS: 00010286
[  170.846808] RAX: 0000000000000000 RBX: ffffffffc03edc60 RCX: 00000000ffffdfff
[  170.847183] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  170.847558] RBP: 0000000000000000 R08: ffffffff89164508 R09: 00000000ffffdfff
[  170.847943] R10: ffffffff89084520 R11: ffffffff89134520 R12: ffffa01f427a65f8
[  170.848332] R13: ffffac8200263e08 R14: ffffa01f427a6b60 R15: ffffffff8a613dd0
[  170.848708] FS:  0000000000000000(0000) GS:ffffa01f7ec80000(0000) knlGS:0000000000000000
[  170.849140] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  170.849455] CR2: 000000000044a3a0 CR3: 00000000029d4002 CR4: 00000000001706f0
[  170.849844] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  170.850222] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  170.850598] Call Trace:
[  170.850734]  <TASK>
[  170.850860] ? __warn (kernel/panic.c:677) 
[  170.851045] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  170.851276] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  170.851483] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  170.851680] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  170.851896] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  170.852132] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  170.852363] br_dev_delete (net/bridge/br_if.c:396) bridge
[  170.852624] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  170.852923] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  170.853123] ? process_one_work (kernel/workqueue.c:2606) 
[  170.853352] process_one_work (kernel/workqueue.c:2638) 
[  170.853579] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  170.853793] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  170.854027] kthread (kernel/kthread.c:388) 
[  170.854211] ? __pfx_kthread (kernel/kthread.c:341) 
[  170.854419] ret_from_fork (arch/x86/kernel/process.c:153) 
[  170.854617] ? __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