======================================
| [ 1346.209379] ------------[ cut here ]------------
| [ 1346.209662] refcount_t: underflow; use-after-free.
| [ 1346.210010] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [ 1346.210615] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel sch_tbf act_pedit macvlan act_mirred cls_flower 8021q bridge stp llc ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress vrf veth
[ 1346.212664] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1346.213567] Workqueue: netns cleanup_net
[ 1346.213895] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1346.214324] 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 6f a1 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 6f a1 	mov    $0xffffffffa16f70a0,%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
[ 1346.215783] RSP: 0018:ffffa91840263d78 EFLAGS: 00010286
[ 1346.216218] RAX: 0000000000000000 RBX: ffff90b982888000 RCX: 00000000ffffdfff
[ 1346.216779] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1346.217355] RBP: ffff90b9828885f8 R08: ffffffffa1b64508 R09: 00000000ffffdfff
[ 1346.217926] R10: ffffffffa1a84520 R11: ffffffffa1b34520 R12: ffff90b982888000
[ 1346.218500] R13: ffffa91840263e08 R14: ffff90b982888b60 R15: ffff90b985d60050
[ 1346.219075] FS:  0000000000000000(0000) GS:ffff90b9bec80000(0000) knlGS:0000000000000000
[ 1346.219686] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1346.220012] CR2: 00007f2f4c663270 CR3: 000000003684c005 CR4: 00000000001706f0
[ 1346.220415] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1346.220803] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1346.221204] Call Trace:
[ 1346.221353]  <TASK>
[ 1346.221483] ? __warn (kernel/panic.c:677) 
[ 1346.221678] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1346.221942] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1346.222161] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1346.222366] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1346.222581] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1346.222816] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1346.223086] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1346.223350] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[ 1346.223651] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1346.223907] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1346.224205] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1346.224418] ? process_one_work (kernel/workqueue.c:2606) 
[ 1346.224657] process_one_work (kernel/workqueue.c:2638) 
[ 1346.224885] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1346.225103] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1346.225367] kthread (kernel/kthread.c:388) 
[ 1346.225555] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1346.225764] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1346.225965] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1346.226190] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1346.229093] ------------[ cut here ]------------
| [ 1346.229456] sysfs group 'bridge' not found for kobject 'br3'
| [ 1346.229924] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1346.230573] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel sch_tbf act_pedit macvlan act_mirred cls_flower 8021q bridge stp llc ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress vrf veth
[ 1346.232751] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1346.233650] Workqueue: netns cleanup_net
[ 1346.233971] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1346.234374] 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 6f a1 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 6f a1 	mov    $0xffffffffa16f0688,%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)
	...
[ 1346.235842] RSP: 0018:ffffa91840263d70 EFLAGS: 00010286
[ 1346.236265] RAX: 0000000000000000 RBX: ffffffffc04aec60 RCX: 00000000ffffdfff
[ 1346.236762] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1346.237153] RBP: 0000000000000000 R08: ffffffffa1b64508 R09: 00000000ffffdfff
[ 1346.237556] R10: ffffffffa1a84520 R11: ffffffffa1b34520 R12: ffff90b9828885f8
[ 1346.237936] R13: ffffa91840263e08 R14: ffff90b982888b60 R15: ffff90b985d60050
[ 1346.238336] FS:  0000000000000000(0000) GS:ffff90b9bec80000(0000) knlGS:0000000000000000
[ 1346.238775] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1346.239094] CR2: 00007f2f4c663270 CR3: 000000003684c005 CR4: 00000000001706f0
[ 1346.239511] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1346.239893] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1346.240291] Call Trace:
[ 1346.240432]  <TASK>
[ 1346.240557] ? __warn (kernel/panic.c:677) 
[ 1346.240742] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1346.240985] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1346.241198] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1346.241405] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1346.241619] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1346.241861] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1346.242103] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1346.242381] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1346.242672] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1346.242877] ? process_one_work (kernel/workqueue.c:2606) 
[ 1346.243119] process_one_work (kernel/workqueue.c:2638) 
[ 1346.243352] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1346.243561] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1346.243802] kthread (kernel/kthread.c:388) 
[ 1346.243989] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1346.244200] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1346.244432] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1346.244642] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1346.348187] ------------[ cut here ]------------
| [ 1346.348467] sysfs group 'bridge' not found for kobject 'br3'
| [ 1346.348870] WARNING: CPU: 3 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1346.349335] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel sch_tbf act_pedit macvlan act_mirred cls_flower 8021q bridge stp llc ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress vrf veth
[ 1346.350827] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1346.351463] Workqueue: netns cleanup_net
[ 1346.351713] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1346.352004] 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 6f a1 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 6f a1 	mov    $0xffffffffa16f0688,%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)
	...
[ 1346.353032] RSP: 0018:ffffa91840263d70 EFLAGS: 00010286
[ 1346.353372] RAX: 0000000000000000 RBX: ffffffffc04aec60 RCX: 00000000ffffdfff
[ 1346.353765] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1346.354159] RBP: 0000000000000000 R08: ffffffffa1b64508 R09: 00000000ffffdfff
[ 1346.354567] R10: ffffffffa1a84520 R11: ffffffffa1b34520 R12: ffff90b982bb45f8
[ 1346.354970] R13: ffffa91840263e08 R14: ffff90b982bb4b60 R15: ffffffffa3013dd0
[ 1346.355394] FS:  0000000000000000(0000) GS:ffff90b9bed80000(0000) knlGS:0000000000000000
[ 1346.355872] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1346.356241] CR2: 00005637a6bfbdec CR3: 0000000002a06001 CR4: 00000000001706f0
[ 1346.356645] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1346.357043] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1346.357435] Call Trace:
[ 1346.357581]  <TASK>
[ 1346.357708] ? __warn (kernel/panic.c:677) 
[ 1346.357903] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1346.358144] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1346.358368] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1346.358563] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1346.358789] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1346.359036] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1346.359285] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1346.359574] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1346.359877] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1346.360099] ? process_one_work (kernel/workqueue.c:2606) 
[ 1346.360332] process_one_work (kernel/workqueue.c:2638) 
[ 1346.360557] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1346.360765] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1346.361012] kthread (kernel/kthread.c:388) 
[ 1346.361192] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1346.361408] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1346.361610] ? __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