======================================
| [  170.871734] ------------[ cut here ]------------
| [  170.872025] refcount_t: underflow; use-after-free.
| [  170.872316] WARNING: CPU: 0 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  170.872761] Modules linked in: macvlan 8021q vxlan ip6_udp_tunnel udp_tunnel dummy act_mirred cls_flower bridge stp llc ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress vrf veth
[  170.874149] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  170.874769] Workqueue: netns cleanup_net
[  170.874998] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 170.875288] 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 ac 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 ac 	mov    $0xffffffffac8f70a0,%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
[  170.876267] RSP: 0018:ffffa9ea40063d78 EFLAGS: 00010286
[  170.876554] RAX: 0000000000000000 RBX: ffff89e0c3f6a000 RCX: 00000000ffffdfff
[  170.876943] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  170.877333] RBP: ffff89e0c3f6a5f8 R08: ffffffffacd64508 R09: 00000000ffffdfff
[  170.877709] R10: ffffffffacc84520 R11: ffffffffacd34520 R12: ffff89e0c3f6a000
[  170.878104] R13: ffffa9ea40063e08 R14: ffff89e0c3f6ab60 R15: ffffffffae213dd0
[  170.878481] FS:  0000000000000000(0000) GS:ffff89e0fec00000(0000) knlGS:0000000000000000
[  170.878923] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  170.879243] CR2: 00005561d509ceb8 CR3: 0000000009a4c001 CR4: 00000000001706f0
[  170.879621] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  170.880004] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  170.880387] Call Trace:
[  170.880528]  <TASK>
[  170.880655] ? __warn (kernel/panic.c:677) 
[  170.880855] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  170.881108] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  170.881319] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  170.881517] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  170.881731] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  170.881974] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  170.882230] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  170.882482] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  170.882786] br_dev_delete (net/bridge/br_if.c:396) bridge
[  170.883049] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  170.883356] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  170.883559] ? process_one_work (kernel/workqueue.c:2606) 
[  170.883790] process_one_work (kernel/workqueue.c:2638) 
[  170.884021] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  170.884230] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  170.884464] kthread (kernel/kthread.c:388) 
[  170.884646] ? __pfx_kthread (kernel/kthread.c:341) 
[  170.884862] ret_from_fork (arch/x86/kernel/process.c:153) 
[  170.885063] ? __pfx_kthread (kernel/kthread.c:341) 
[  170.885273] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  170.888232] ------------[ cut here ]------------
| [  170.888623] sysfs group 'bridge' not found for kobject 'br1'
| [  170.889109] WARNING: CPU: 2 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  170.889752] Modules linked in: macvlan 8021q vxlan ip6_udp_tunnel udp_tunnel dummy act_mirred cls_flower bridge stp llc ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress vrf veth
[  170.891879] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  170.892771] Workqueue: netns cleanup_net
[  170.893108] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 170.893500] 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 ac 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 ac 	mov    $0xffffffffac8f0688,%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)
	...
[  170.894965] RSP: 0018:ffffa9ea40063d70 EFLAGS: 00010286
[  170.895376] RAX: 0000000000000000 RBX: ffffffffc02e9c60 RCX: 00000000ffffdfff
[  170.895948] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  170.896335] RBP: 0000000000000000 R08: ffffffffacd64508 R09: 00000000ffffdfff
[  170.896719] R10: ffffffffacc84520 R11: ffffffffacd34520 R12: ffff89e0c3f6a5f8
[  170.897120] R13: ffffa9ea40063e08 R14: ffff89e0c3f6ab60 R15: ffffffffae213dd0
[  170.897525] FS:  0000000000000000(0000) GS:ffff89e0fed00000(0000) knlGS:0000000000000000
[  170.897961] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  170.898279] CR2: 00007fcd475111b4 CR3: 0000000009a4c001 CR4: 00000000001706f0
[  170.898656] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  170.899047] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  170.899435] Call Trace:
[  170.899573]  <TASK>
[  170.899700] ? __warn (kernel/panic.c:677) 
[  170.899891] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  170.900139] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  170.900344] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  170.900537] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  170.900927] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  170.901184] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  170.901426] br_dev_delete (net/bridge/br_if.c:396) bridge
[  170.901700] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  170.902001] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  170.902210] ? process_one_work (kernel/workqueue.c:2606) 
[  170.902442] process_one_work (kernel/workqueue.c:2638) 
[  170.902668] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  170.902886] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  170.903131] kthread (kernel/kthread.c:388) 
[  170.903304] ? __pfx_kthread (kernel/kthread.c:341) 
[  170.903509] ret_from_fork (arch/x86/kernel/process.c:153) 
[  170.903711] ? __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