======================================
| [ 1135.388174] ------------[ cut here ]------------
| [ 1135.388447] refcount_t: underflow; use-after-free.
| [ 1135.388759] WARNING: CPU: 2 PID: 66 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [ 1135.389223] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[ 1135.390534] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1135.391247] Workqueue: netns cleanup_net
[ 1135.391508] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1135.391846] 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 84 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 84 	mov    $0xffffffff84cf70a0,%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
[ 1135.392988] RSP: 0018:ffffaad400253d78 EFLAGS: 00010286
[ 1135.393333] RAX: 0000000000000000 RBX: ffff96c342414000 RCX: 00000000ffffdfff
[ 1135.393776] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1135.394239] RBP: ffff96c3424145f8 R08: ffffffff85164508 R09: 00000000ffffdfff
[ 1135.394690] R10: ffffffff85084520 R11: ffffffff85134520 R12: ffff96c342414000
[ 1135.395150] R13: ffffaad400253e08 R14: ffff96c342414b60 R15: ffff96c342b00050
[ 1135.395608] FS:  0000000000000000(0000) GS:ffff96c37ed00000(0000) knlGS:0000000000000000
[ 1135.396109] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1135.396417] CR2: 0000561210f76dec CR3: 000000000580c005 CR4: 00000000001706f0
[ 1135.396800] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1135.397194] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1135.397572] Call Trace:
[ 1135.397712]  <TASK>
[ 1135.397844] ? __warn (kernel/panic.c:677) 
[ 1135.398033] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1135.398286] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1135.398494] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1135.398692] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1135.398908] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1135.399143] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1135.399399] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1135.399660] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[ 1135.399962] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1135.400218] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1135.400510] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1135.400712] ? process_one_work (kernel/workqueue.c:2606) 
[ 1135.400954] process_one_work (kernel/workqueue.c:2638) 
[ 1135.401182] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1135.401390] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1135.401624] kthread (kernel/kthread.c:388) 
[ 1135.401803] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1135.402018] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1135.402218] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1135.402426] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1135.405085] ------------[ cut here ]------------
| [ 1135.405353] sysfs group 'bridge' not found for kobject 'br2'
| [ 1135.405680] WARNING: CPU: 1 PID: 66 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1135.406136] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[ 1135.407363] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1135.407972] Workqueue: netns cleanup_net
[ 1135.408194] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1135.408461] 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 84 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 84 	mov    $0xffffffff84cf0688,%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)
	...
[ 1135.409449] RSP: 0018:ffffaad400253d70 EFLAGS: 00010286
[ 1135.409746] RAX: 0000000000000000 RBX: ffffffffc065ac60 RCX: 00000000ffffdfff
[ 1135.410135] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1135.410521] RBP: 0000000000000000 R08: ffffffff85164508 R09: 00000000ffffdfff
[ 1135.410910] R10: ffffffff85084520 R11: ffffffff85134520 R12: ffff96c3424145f8
[ 1135.411292] R13: ffffaad400253e08 R14: ffff96c342414b60 R15: ffff96c342b00050
[ 1135.411691] FS:  0000000000000000(0000) GS:ffff96c37ec80000(0000) knlGS:0000000000000000
[ 1135.412133] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1135.412442] CR2: 000055b649190638 CR3: 0000000002bcc001 CR4: 00000000001706f0
[ 1135.412822] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1135.413205] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1135.413589] Call Trace:
[ 1135.413735]  <TASK>
[ 1135.413863] ? __warn (kernel/panic.c:677) 
[ 1135.414052] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1135.414282] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1135.414491] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1135.414687] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1135.414905] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1135.415143] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1135.415374] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1135.415634] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1135.415929] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1135.416136] ? process_one_work (kernel/workqueue.c:2606) 
[ 1135.416366] process_one_work (kernel/workqueue.c:2638) 
[ 1135.416587] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1135.416797] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1135.417040] kthread (kernel/kthread.c:388) 
[ 1135.417218] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1135.417425] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1135.417629] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1135.417844] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1135.529068] ------------[ cut here ]------------
| [ 1135.529344] sysfs group 'bridge' not found for kobject 'br2'
| [ 1135.529783] WARNING: CPU: 0 PID: 66 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1135.530248] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[ 1135.531489] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1135.532132] Workqueue: netns cleanup_net
[ 1135.532361] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1135.532636] 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 84 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 84 	mov    $0xffffffff84cf0688,%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)
	...
[ 1135.533671] RSP: 0018:ffffaad400253d70 EFLAGS: 00010286
[ 1135.533968] RAX: 0000000000000000 RBX: ffffffffc065ac60 RCX: 00000000ffffdfff
[ 1135.534366] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1135.534772] RBP: 0000000000000000 R08: ffffffff85164508 R09: 00000000ffffdfff
[ 1135.535181] R10: ffffffff85084520 R11: ffffffff85134520 R12: ffff96c3428505f8
[ 1135.535584] R13: ffffaad400253e08 R14: ffff96c342850b60 R15: ffffffff86613dd0
[ 1135.536001] FS:  0000000000000000(0000) GS:ffff96c37ec00000(0000) knlGS:0000000000000000
[ 1135.536475] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1135.536819] CR2: 00000000004e1f90 CR3: 0000000005e6c002 CR4: 00000000001706f0
[ 1135.537242] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1135.537659] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1135.538070] Call Trace:
[ 1135.538218]  <TASK>
[ 1135.538351] ? __warn (kernel/panic.c:677) 
[ 1135.538545] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1135.538799] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1135.539035] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1135.539251] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1135.539489] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1135.539743] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1135.540013] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1135.540300] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1135.540621] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1135.540849] ? process_one_work (kernel/workqueue.c:2606) 
[ 1135.541099] process_one_work (kernel/workqueue.c:2638) 
[ 1135.541332] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1135.541559] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1135.541802] kthread (kernel/kthread.c:388) 
[ 1135.542004] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1135.542221] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1135.542444] ? __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