======================================
| [   12.511559] ------------[ cut here ]------------
| [   12.511904] refcount_t: underflow; use-after-free.
| [   12.512277] WARNING: CPU: 0 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [   12.512876] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[   12.514063] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.514823] Workqueue: netns cleanup_net
[   12.515063] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 12.515359] 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 aa 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 aa 	mov    $0xffffffffaa6f70a0,%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
[   12.516373] RSP: 0018:ffffa7cb40063d78 EFLAGS: 00010286
[   12.516666] RAX: 0000000000000000 RBX: ffff8d0c028b4000 RCX: 00000000ffffdfff
[   12.517058] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.517470] RBP: ffff8d0c028b45f8 R08: ffffffffaab64508 R09: 00000000ffffdfff
[   12.517854] R10: ffffffffaaa84520 R11: ffffffffaab34520 R12: ffff8d0c028b4000
[   12.518237] R13: ffffa7cb40063e08 R14: ffff8d0c028b4b60 R15: ffff8d0c03b50050
[   12.518635] FS:  0000000000000000(0000) GS:ffff8d0c3ec00000(0000) knlGS:0000000000000000
[   12.519069] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.519384] CR2: 00005642c8760918 CR3: 00000000029cc001 CR4: 00000000001706f0
[   12.519770] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.520160] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.520557] Call Trace:
[   12.520700]  <TASK>
[   12.520824] ? __warn (kernel/panic.c:677) 
[   12.521008] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.521267] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.521482] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.521681] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.521892] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.522128] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.522391] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   12.522649] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[   12.522949] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.523208] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.523510] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.523715] ? process_one_work (kernel/workqueue.c:2606) 
[   12.523951] process_one_work (kernel/workqueue.c:2638) 
[   12.524179] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.524397] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.524634] kthread (kernel/kthread.c:388) 
[   12.524823] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.525031] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.525236] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.525448] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   12.528382] ------------[ cut here ]------------
| [   12.528714] sysfs group 'bridge' not found for kobject 'br2'
| [   12.529115] WARNING: CPU: 0 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   12.529699] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[   12.531001] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.531794] Workqueue: netns cleanup_net
[   12.532086] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 12.532458] 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 aa 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 aa 	mov    $0xffffffffaa6f0688,%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)
	...
[   12.533709] RSP: 0018:ffffa7cb40063d70 EFLAGS: 00010286
[   12.534046] RAX: 0000000000000000 RBX: ffffffffc03aec60 RCX: 00000000ffffdfff
[   12.534530] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.534928] RBP: 0000000000000000 R08: ffffffffaab64508 R09: 00000000ffffdfff
[   12.535325] R10: ffffffffaaa84520 R11: ffffffffaab34520 R12: ffff8d0c028b45f8
[   12.535740] R13: ffffa7cb40063e08 R14: ffff8d0c028b4b60 R15: ffff8d0c03b50050
[   12.536170] FS:  0000000000000000(0000) GS:ffff8d0c3ec00000(0000) knlGS:0000000000000000
[   12.536612] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.536949] CR2: 00005642c8760918 CR3: 00000000029cc001 CR4: 00000000001706f0
[   12.537437] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.537888] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.538321] Call Trace:
[   12.538496]  <TASK>
[   12.538635] ? __warn (kernel/panic.c:677) 
[   12.538873] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.539164] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.539435] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.539688] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.539951] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.540255] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.540558] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.540897] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.541267] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.541533] ? process_one_work (kernel/workqueue.c:2606) 
[   12.541832] process_one_work (kernel/workqueue.c:2638) 
[   12.542112] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.542394] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.542691] kthread (kernel/kthread.c:388) 
[   12.542924] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.543188] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.543469] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.543739] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   12.649526] ------------[ cut here ]------------
| [   12.649805] sysfs group 'bridge' not found for kobject 'br2'
| [   12.650137] WARNING: CPU: 0 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   12.650607] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel bridge stp llc 8021q sch_ingress vrf veth
[   12.651636] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   12.652261] Workqueue: netns cleanup_net
[   12.652496] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 12.652766] 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 aa 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 aa 	mov    $0xffffffffaa6f0688,%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)
	...
[   12.653778] RSP: 0018:ffffa7cb40063d70 EFLAGS: 00010286
[   12.654071] RAX: 0000000000000000 RBX: ffffffffc03aec60 RCX: 00000000ffffdfff
[   12.654473] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   12.654896] RBP: 0000000000000000 R08: ffffffffaab64508 R09: 00000000ffffdfff
[   12.655471] R10: ffffffffaaa84520 R11: ffffffffaab34520 R12: ffff8d0c0190e5f8
[   12.656026] R13: ffffa7cb40063e08 R14: ffff8d0c0190eb60 R15: ffffffffac013dd0
[   12.656594] FS:  0000000000000000(0000) GS:ffff8d0c3ec00000(0000) knlGS:0000000000000000
[   12.657224] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.657693] CR2: 00007f4927094000 CR3: 0000000023a4c006 CR4: 00000000001706f0
[   12.658261] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.658838] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   12.659419] Call Trace:
[   12.659622]  <TASK>
[   12.659803] ? __warn (kernel/panic.c:677) 
[   12.660083] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.660451] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   12.660767] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   12.661075] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   12.661421] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   12.661793] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   12.662157] br_dev_delete (net/bridge/br_if.c:396) bridge
[   12.662582] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[   12.663038] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[   12.663360] ? process_one_work (kernel/workqueue.c:2606) 
[   12.663710] process_one_work (kernel/workqueue.c:2638) 
[   12.664052] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   12.664382] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   12.664738] kthread (kernel/kthread.c:388) 
[   12.665038] ? __pfx_kthread (kernel/kthread.c:341) 
[   12.665248] ret_from_fork (arch/x86/kernel/process.c:153) 
[   12.665463] ? __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