======================================
| [ 1299.827257] ------------[ cut here ]------------
| [ 1299.827577] refcount_t: underflow; use-after-free.
| [ 1299.827867] WARNING: CPU: 2 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [ 1299.828338] Modules linked in: macvlan vxlan ip6_udp_tunnel udp_tunnel act_vlan 8021q dummy act_mirred ip6_gre ip6_tunnel tunnel6 cls_matchall ip_gre gre act_gact cls_flower sch_ingress bridge stp llc vrf veth
[ 1299.829752] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1299.830387] Workqueue: netns cleanup_net
[ 1299.830611] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1299.830895] 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 8f a6 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 8f a6 	mov    $0xffffffffa68f70c8,%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
[ 1299.831957] RSP: 0018:ffff979fc0263d78 EFLAGS: 00010286
[ 1299.832244] RAX: 0000000000000000 RBX: ffff8a54425fe000 RCX: 00000000ffffdfff
[ 1299.832624] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1299.833009] RBP: ffff8a54425fe5f8 R08: ffffffffa6d64508 R09: 00000000ffffdfff
[ 1299.833388] R10: ffffffffa6c84520 R11: ffffffffa6d34520 R12: ffff8a54425fe000
[ 1299.833764] R13: ffff979fc0263e08 R14: ffff8a54425feb60 R15: ffffffffa8213dd0
[ 1299.834150] FS:  0000000000000000(0000) GS:ffff8a547ed00000(0000) knlGS:0000000000000000
[ 1299.834577] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1299.834905] CR2: 00005558e7491588 CR3: 0000000001f1c004 CR4: 00000000001706f0
[ 1299.835424] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1299.835974] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1299.836409] Call Trace:
[ 1299.836552]  <TASK>
[ 1299.836703] ? __warn (kernel/panic.c:677) 
[ 1299.836889] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1299.837163] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1299.837373] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1299.837571] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1299.837790] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1299.838050] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1299.838308] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1299.838562] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[ 1299.838865] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1299.839144] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1299.839467] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1299.839669] ? process_one_work (kernel/workqueue.c:2606) 
[ 1299.839902] process_one_work (kernel/workqueue.c:2638) 
[ 1299.840143] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1299.840353] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1299.840618] kthread (kernel/kthread.c:388) 
[ 1299.840792] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1299.841013] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1299.841219] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1299.841424] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1299.844187] ------------[ cut here ]------------
| [ 1299.844471] sysfs group 'bridge' not found for kobject 'br1'
| [ 1299.844795] WARNING: CPU: 2 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1299.845248] Modules linked in: macvlan vxlan ip6_udp_tunnel udp_tunnel act_vlan 8021q dummy act_mirred ip6_gre ip6_tunnel tunnel6 cls_matchall ip_gre gre act_gact cls_flower sch_ingress bridge stp llc vrf veth
[ 1299.846796] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1299.847451] Workqueue: netns cleanup_net
[ 1299.847671] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1299.847934] 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 8f a6 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 8f a6 	mov    $0xffffffffa68f06b0,%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)
	...
[ 1299.848956] RSP: 0018:ffff979fc0263d70 EFLAGS: 00010286
[ 1299.849245] RAX: 0000000000000000 RBX: ffffffffc02b3c60 RCX: 00000000ffffdfff
[ 1299.849620] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1299.850009] RBP: 0000000000000000 R08: ffffffffa6d64508 R09: 00000000ffffdfff
[ 1299.850388] R10: ffffffffa6c84520 R11: ffffffffa6d34520 R12: ffff8a54425fe5f8
[ 1299.850764] R13: ffff979fc0263e08 R14: ffff8a54425feb60 R15: ffffffffa8213dd0
[ 1299.851162] FS:  0000000000000000(0000) GS:ffff8a547ed00000(0000) knlGS:0000000000000000
[ 1299.851617] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1299.851930] CR2: 00005558e7491588 CR3: 0000000001f1c004 CR4: 00000000001706f0
[ 1299.852323] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1299.852728] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1299.853109] Call Trace:
[ 1299.853247]  <TASK>
[ 1299.853369] ? __warn (kernel/panic.c:677) 
[ 1299.853551] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1299.853784] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1299.854000] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1299.854200] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1299.854411] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1299.854650] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1299.854883] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1299.855170] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1299.855501] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1299.855705] ? process_one_work (kernel/workqueue.c:2606) 
[ 1299.855933] process_one_work (kernel/workqueue.c:2638) 
[ 1299.856166] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1299.856373] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1299.856639] kthread (kernel/kthread.c:388) 
[ 1299.856817] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1299.857032] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1299.857233] ? __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