======================================
| [  328.288225] ------------[ cut here ]------------
| [  328.288638] refcount_t: underflow; use-after-free.
| [  328.289045] WARNING: CPU: 2 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  328.289721] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel dummy act_pedit act_mirred cls_flower 8021q ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress bridge stp llc vrf veth
[  328.292142] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  328.293061] Workqueue: netns cleanup_net
[  328.293403] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 328.293826] 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 8f 9c 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 8f 9c 	mov    $0xffffffff9c8f70c8,%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
[  328.295301] RSP: 0018:ffffb40fc0063d78 EFLAGS: 00010286
[  328.295730] RAX: 0000000000000000 RBX: ffff8fcbc190e000 RCX: 00000000ffffdfff
[  328.296318] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  328.296887] RBP: ffff8fcbc190e5f8 R08: ffffffff9cd64508 R09: 00000000ffffdfff
[  328.297484] R10: ffffffff9cc84520 R11: ffffffff9cd34520 R12: ffff8fcbc190e000
[  328.298060] R13: ffffb40fc0063e08 R14: ffff8fcbc190eb60 R15: ffff8fcbc4d38050
[  328.298643] FS:  0000000000000000(0000) GS:ffff8fcbfed00000(0000) knlGS:0000000000000000
[  328.299303] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  328.299759] CR2: 00007ff1c95831b4 CR3: 0000000039a4c004 CR4: 00000000001706f0
[  328.300344] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  328.300919] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  328.301505] Call Trace:
[  328.301716]  <TASK>
[  328.301904] ? __warn (kernel/panic.c:677) 
[  328.302182] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  328.302577] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  328.302888] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  328.303180] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  328.303514] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  328.303869] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  328.304264] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  328.304650] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  328.305082] br_dev_delete (net/bridge/br_if.c:396) bridge
[  328.305484] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  328.305930] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  328.306247] ? process_one_work (kernel/workqueue.c:2606) 
[  328.306596] process_one_work (kernel/workqueue.c:2638) 
[  328.306933] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  328.307264] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  328.307622] kthread (kernel/kthread.c:388) 
[  328.307888] ? __pfx_kthread (kernel/kthread.c:341) 
[  328.308212] ret_from_fork (arch/x86/kernel/process.c:153) 
[  328.308515] ? __pfx_kthread (kernel/kthread.c:341) 
[  328.308824] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  328.312764] ------------[ cut here ]------------
| [  328.313142] sysfs group 'bridge' not found for kobject 'br2'
| [  328.313631] WARNING: CPU: 2 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  328.314275] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel dummy act_pedit act_mirred cls_flower 8021q ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress bridge stp llc vrf veth
[  328.316391] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  328.317301] Workqueue: netns cleanup_net
[  328.317622] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 328.318012] 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 8f 9c 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 8f 9c 	mov    $0xffffffff9c8f06b0,%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)
	...
[  328.319482] RSP: 0018:ffffb40fc0063d70 EFLAGS: 00010286
[  328.319904] RAX: 0000000000000000 RBX: ffffffffc04d9c60 RCX: 00000000ffffdfff
[  328.320486] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  328.321052] RBP: 0000000000000000 R08: ffffffff9cd64508 R09: 00000000ffffdfff
[  328.321638] R10: ffffffff9cc84520 R11: ffffffff9cd34520 R12: ffff8fcbc190e5f8
[  328.322216] R13: ffffb40fc0063e08 R14: ffff8fcbc190eb60 R15: ffff8fcbc4d38050
[  328.322787] FS:  0000000000000000(0000) GS:ffff8fcbfed00000(0000) knlGS:0000000000000000
[  328.323451] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  328.323919] CR2: 00007ff1c95831b4 CR3: 0000000039a4c004 CR4: 00000000001706f0
[  328.324504] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  328.325076] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  328.325656] Call Trace:
[  328.325870]  <TASK>
[  328.326049] ? __warn (kernel/panic.c:677) 
[  328.326329] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  328.326675] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  328.326991] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  328.327311] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  328.327623] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  328.327972] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  328.328335] br_dev_delete (net/bridge/br_if.c:396) bridge
[  328.328725] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  328.329161] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  328.329480] ? process_one_work (kernel/workqueue.c:2606) 
[  328.329812] process_one_work (kernel/workqueue.c:2638) 
[  328.330147] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  328.330470] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  328.330822] kthread (kernel/kthread.c:388) 
[  328.331086] ? __pfx_kthread (kernel/kthread.c:341) 
[  328.331411] ret_from_fork (arch/x86/kernel/process.c:153) 
[  328.331713] ? __pfx_kthread (kernel/kthread.c:341) 
[  328.332028] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  328.457422] ------------[ cut here ]------------
| [  328.457712] sysfs group 'bridge' not found for kobject 'br2'
| [  328.458056] WARNING: CPU: 2 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  328.458557] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel dummy act_pedit act_mirred cls_flower 8021q ip6_gre ip6_tunnel tunnel6 act_gact cls_matchall ip_gre gre sch_ingress bridge stp llc vrf veth
[  328.460100] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  328.460756] Workqueue: netns cleanup_net
[  328.460978] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 328.461247] 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 8f 9c 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 8f 9c 	mov    $0xffffffff9c8f06b0,%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)
	...
[  328.462243] RSP: 0018:ffffb40fc0063d70 EFLAGS: 00010286
[  328.462559] RAX: 0000000000000000 RBX: ffffffffc04d9c60 RCX: 00000000ffffdfff
[  328.462940] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  328.463328] RBP: 0000000000000000 R08: ffffffff9cd64508 R09: 00000000ffffdfff
[  328.463717] R10: ffffffff9cc84520 R11: ffffffff9cd34520 R12: ffff8fcbc190c5f8
[  328.464113] R13: ffffb40fc0063e08 R14: ffff8fcbc190cb60 R15: ffffffff9e213dd0
[  328.464533] FS:  0000000000000000(0000) GS:ffff8fcbfed00000(0000) knlGS:0000000000000000
[  328.465027] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  328.465363] CR2: 000056140a638dec CR3: 0000000002fb4006 CR4: 00000000001706f0
[  328.465777] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  328.466159] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  328.466592] Call Trace:
[  328.466743]  <TASK>
[  328.466877] ? __warn (kernel/panic.c:677) 
[  328.467074] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  328.467370] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  328.467609] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  328.467811] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  328.468040] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  328.468307] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  328.468573] br_dev_delete (net/bridge/br_if.c:396) bridge
[  328.468838] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  328.469132] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  328.469342] ? process_one_work (kernel/workqueue.c:2606) 
[  328.469637] process_one_work (kernel/workqueue.c:2638) 
[  328.469935] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  328.470146] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  328.470391] kthread (kernel/kthread.c:388) 
[  328.470586] ? __pfx_kthread (kernel/kthread.c:341) 
[  328.470818] ret_from_fork (arch/x86/kernel/process.c:153) 
[  328.471037] ? __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