======================================
| [ 1250.194174] ------------[ cut here ]------------
| [ 1250.194464] refcount_t: underflow; use-after-free.
| [ 1250.194763] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [ 1250.195308] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel sch_prio act_gact cls_flower sch_ingress act_mirred cls_matchall sch_red dummy sch_tbf bridge stp llc 8021q vrf veth
[ 1250.196669] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1250.197284] Workqueue: netns cleanup_net
[ 1250.197510] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1250.197812] 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 af 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 af b9 	mov    $0xffffffffb9af70c8,%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
[ 1250.198795] RSP: 0018:ffffbec900263d78 EFLAGS: 00010286
[ 1250.199101] RAX: 0000000000000000 RBX: ffff99c0025be000 RCX: 00000000ffffdfff
[ 1250.199489] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1250.199865] RBP: ffff99c0025be5f8 R08: ffffffffb9f64508 R09: 00000000ffffdfff
[ 1250.200255] R10: ffffffffb9e84520 R11: ffffffffb9f34520 R12: ffff99c0025be000
[ 1250.200635] R13: ffffbec900263e08 R14: ffff99c0025beb60 R15: ffff99c0063c8050
[ 1250.201023] FS:  0000000000000000(0000) GS:ffff99c03ec80000(0000) knlGS:0000000000000000
[ 1250.201459] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1250.201767] CR2: 00007f15bf025000 CR3: 000000002664c001 CR4: 00000000001706f0
[ 1250.202172] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1250.202563] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1250.202958] Call Trace:
[ 1250.203105]  <TASK>
[ 1250.203244] ? __warn (kernel/panic.c:677) 
[ 1250.203434] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1250.203702] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1250.203916] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1250.204124] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1250.204336] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1250.204581] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1250.204841] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1250.205108] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[ 1250.205418] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1250.205685] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1250.205985] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1250.206197] ? process_one_work (kernel/workqueue.c:2606) 
[ 1250.206439] process_one_work (kernel/workqueue.c:2638) 
[ 1250.206665] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1250.206887] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1250.207130] kthread (kernel/kthread.c:388) 
[ 1250.207317] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1250.207526] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1250.207736] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1250.207953] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1250.210650] ------------[ cut here ]------------
| [ 1250.210923] sysfs group 'bridge' not found for kobject 'br2'
| [ 1250.211250] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1250.211691] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel sch_prio act_gact cls_flower sch_ingress act_mirred cls_matchall sch_red dummy sch_tbf bridge stp llc 8021q vrf veth
[ 1250.213045] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1250.213659] Workqueue: netns cleanup_net
[ 1250.213875] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1250.214140] 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 af 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 af b9 	mov    $0xffffffffb9af06b0,%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)
	...
[ 1250.215147] RSP: 0018:ffffbec900263d70 EFLAGS: 00010286
[ 1250.215432] RAX: 0000000000000000 RBX: ffffffffc0496c60 RCX: 00000000ffffdfff
[ 1250.215830] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1250.216230] RBP: 0000000000000000 R08: ffffffffb9f64508 R09: 00000000ffffdfff
[ 1250.216625] R10: ffffffffb9e84520 R11: ffffffffb9f34520 R12: ffff99c0025be5f8
[ 1250.217021] R13: ffffbec900263e08 R14: ffff99c0025beb60 R15: ffff99c0063c8050
[ 1250.217426] FS:  0000000000000000(0000) GS:ffff99c03ec80000(0000) knlGS:0000000000000000
[ 1250.217880] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1250.218210] CR2: 00007f15bf025000 CR3: 000000002664c001 CR4: 00000000001706f0
[ 1250.218604] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1250.218997] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1250.219397] Call Trace:
[ 1250.219545]  <TASK>
[ 1250.219678] ? __warn (kernel/panic.c:677) 
[ 1250.219873] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1250.220115] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1250.220333] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1250.220527] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1250.220742] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1250.220987] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1250.221225] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1250.221486] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1250.221784] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1250.221996] ? process_one_work (kernel/workqueue.c:2606) 
[ 1250.222236] process_one_work (kernel/workqueue.c:2638) 
[ 1250.222459] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1250.222692] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1250.222938] kthread (kernel/kthread.c:388) 
[ 1250.223127] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1250.223350] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1250.223581] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1250.223806] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1250.336141] ------------[ cut here ]------------
| [ 1250.336442] sysfs group 'bridge' not found for kobject 'br2'
| [ 1250.336766] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1250.337228] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel sch_prio act_gact cls_flower sch_ingress act_mirred cls_matchall sch_red dummy sch_tbf bridge stp llc 8021q vrf veth
[ 1250.338570] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1250.339182] Workqueue: netns cleanup_net
[ 1250.339479] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1250.339852] 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 af 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 af b9 	mov    $0xffffffffb9af06b0,%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)
	...
[ 1250.341247] RSP: 0018:ffffbec900263d70 EFLAGS: 00010286
[ 1250.341662] RAX: 0000000000000000 RBX: ffffffffc0496c60 RCX: 00000000ffffdfff
[ 1250.342224] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1250.342785] RBP: 0000000000000000 R08: ffffffffb9f64508 R09: 00000000ffffdfff
[ 1250.343349] R10: ffffffffb9e84520 R11: ffffffffb9f34520 R12: ffff99c0025ba5f8
[ 1250.343915] R13: ffffbec900263e08 R14: ffff99c0025bab60 R15: ffffffffbb413dd0
[ 1250.344472] FS:  0000000000000000(0000) GS:ffff99c03ec80000(0000) knlGS:0000000000000000
[ 1250.345104] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1250.345546] CR2: 00007f15bf025000 CR3: 000000002664c001 CR4: 00000000001706f0
[ 1250.346108] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1250.346664] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1250.347234] Call Trace:
[ 1250.347438]  <TASK>
[ 1250.347626] ? __warn (kernel/panic.c:677) 
[ 1250.347890] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1250.348242] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1250.348542] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1250.348827] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1250.349143] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1250.349485] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1250.349820] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1250.350219] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1250.350647] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1250.350962] ? process_one_work (kernel/workqueue.c:2606) 
[ 1250.351295] process_one_work (kernel/workqueue.c:2638) 
[ 1250.351617] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1250.351930] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1250.352269] kthread (kernel/kthread.c:388) 
[ 1250.352525] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1250.352837] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1250.353143] ? __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