======================================
| [ 1339.790202] ------------[ cut here ]------------
| [ 1339.790574] refcount_t: underflow; use-after-free.
| [ 1339.790917] WARNING: CPU: 1 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [ 1339.791504] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_skbedit sch_prio ip6_gre ip6_tunnel tunnel6 cls_matchall act_mirred dummy bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[ 1339.793246] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1339.794002] Workqueue: netns cleanup_net
[ 1339.794291] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1339.794599] 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 cf 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 cf b9 	mov    $0xffffffffb9cf70c8,%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
[ 1339.795898] RSP: 0018:ffffb4f30025bd78 EFLAGS: 00010286
[ 1339.796295] RAX: 0000000000000000 RBX: ffff8c270190c000 RCX: 00000000ffffdfff
[ 1339.796849] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1339.797418] RBP: ffff8c270190c5f8 R08: ffffffffba164508 R09: 00000000ffffdfff
[ 1339.797988] R10: ffffffffba084520 R11: ffffffffba134520 R12: ffff8c270190c000
[ 1339.798536] R13: ffffb4f30025be08 R14: ffff8c270190cb60 R15: ffff8c2705350050
[ 1339.799104] FS:  0000000000000000(0000) GS:ffff8c273ec80000(0000) knlGS:0000000000000000
[ 1339.799731] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1339.800189] CR2: 00005563fa0678d8 CR3: 000000000507e005 CR4: 00000000001706f0
[ 1339.800745] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1339.801374] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1339.801937] Call Trace:
[ 1339.802140]  <TASK>
[ 1339.802318] ? __warn (kernel/panic.c:677) 
[ 1339.802592] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1339.802972] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1339.803277] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1339.803566] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1339.803887] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1339.804231] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1339.804521] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1339.804765] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[ 1339.805065] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1339.805320] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1339.805601] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1339.805801] ? process_one_work (kernel/workqueue.c:2606) 
[ 1339.806032] process_one_work (kernel/workqueue.c:2638) 
[ 1339.806263] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1339.806464] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1339.806696] kthread (kernel/kthread.c:388) 
[ 1339.806875] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1339.807077] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1339.807297] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1339.807498] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1339.810080] ------------[ cut here ]------------
| [ 1339.810338] sysfs group 'bridge' not found for kobject 'br2'
| [ 1339.810658] WARNING: CPU: 1 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1339.811087] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_skbedit sch_prio ip6_gre ip6_tunnel tunnel6 cls_matchall act_mirred dummy bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[ 1339.812580] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1339.813341] Workqueue: netns cleanup_net
[ 1339.813625] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1339.814003] 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 cf 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 cf b9 	mov    $0xffffffffb9cf06b0,%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)
	...
[ 1339.815421] RSP: 0018:ffffb4f30025bd70 EFLAGS: 00010286
[ 1339.815831] RAX: 0000000000000000 RBX: ffffffffc0650c60 RCX: 00000000ffffdfff
[ 1339.816391] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1339.816959] RBP: 0000000000000000 R08: ffffffffba164508 R09: 00000000ffffdfff
[ 1339.817511] R10: ffffffffba084520 R11: ffffffffba134520 R12: ffff8c270190c5f8
[ 1339.818076] R13: ffffb4f30025be08 R14: ffff8c270190cb60 R15: ffff8c2705350050
[ 1339.818632] FS:  0000000000000000(0000) GS:ffff8c273ec80000(0000) knlGS:0000000000000000
[ 1339.819272] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1339.819728] CR2: 00005563fa0678d8 CR3: 000000000507e005 CR4: 00000000001706f0
[ 1339.820297] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1339.820846] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1339.821417] Call Trace:
[ 1339.821620]  <TASK>
[ 1339.821802] ? __warn (kernel/panic.c:677) 
[ 1339.822079] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1339.822418] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1339.822716] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1339.823013] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1339.823317] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1339.823603] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1339.823829] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1339.824097] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1339.824408] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1339.824608] ? process_one_work (kernel/workqueue.c:2606) 
[ 1339.824830] process_one_work (kernel/workqueue.c:2638) 
[ 1339.825058] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1339.825270] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1339.825501] kthread (kernel/kthread.c:388) 
[ 1339.825675] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1339.825887] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1339.826085] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1339.826292] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1339.931117] ------------[ cut here ]------------
| [ 1339.931421] sysfs group 'bridge' not found for kobject 'br2'
| [ 1339.931749] WARNING: CPU: 2 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1339.932223] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_skbedit sch_prio ip6_gre ip6_tunnel tunnel6 cls_matchall act_mirred dummy bridge stp llc act_gact cls_flower sch_ingress 8021q ip_gre gre vrf veth
[ 1339.933704] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1339.934300] Workqueue: netns cleanup_net
[ 1339.934529] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1339.934790] 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 cf 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 cf b9 	mov    $0xffffffffb9cf06b0,%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)
	...
[ 1339.935773] RSP: 0018:ffffb4f30025bd70 EFLAGS: 00010286
[ 1339.936065] RAX: 0000000000000000 RBX: ffffffffc0650c60 RCX: 00000000ffffdfff
[ 1339.936442] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1339.936820] RBP: 0000000000000000 R08: ffffffffba164508 R09: 00000000ffffdfff
[ 1339.937214] R10: ffffffffba084520 R11: ffffffffba134520 R12: ffff8c27052e85f8
[ 1339.937589] R13: ffffb4f30025be08 R14: ffff8c27052e8b60 R15: ffffffffbb613dd0
[ 1339.937981] FS:  0000000000000000(0000) GS:ffff8c273ed00000(0000) knlGS:0000000000000000
[ 1339.938423] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1339.938732] CR2: 0000000000483ca0 CR3: 0000000002626002 CR4: 00000000001706f0
[ 1339.939135] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1339.939513] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1339.939902] Call Trace:
[ 1339.940048]  <TASK>
[ 1339.940169] ? __warn (kernel/panic.c:677) 
[ 1339.940356] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1339.940587] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1339.940798] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1339.941013] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1339.941284] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1339.941518] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1339.941743] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1339.942024] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1339.942311] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1339.942522] ? process_one_work (kernel/workqueue.c:2606) 
[ 1339.942747] process_one_work (kernel/workqueue.c:2638) 
[ 1339.942978] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1339.943185] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1339.943419] kthread (kernel/kthread.c:388) 
[ 1339.943599] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1339.943801] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1339.944011] ? __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