======================================
| [  534.707252] ------------[ cut here ]------------
| [  534.707647] refcount_t: underflow; use-after-free.
| [  534.708060] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  534.708689] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel sch_ingress em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  534.710330] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  534.711200] Workqueue: netns cleanup_net
[  534.711447] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 534.711732] 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 ba 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 ba 	mov    $0xffffffffba6f70a0,%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
[  534.712738] RSP: 0018:ffffb6d9c0263d78 EFLAGS: 00010286
[  534.713124] RAX: 0000000000000000 RBX: ffff9286c2714000 RCX: 00000000ffffdfff
[  534.713526] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  534.713911] RBP: ffff9286c27145f8 R08: ffffffffbab64508 R09: 00000000ffffdfff
[  534.714371] R10: ffffffffbaa84520 R11: ffffffffbab34520 R12: ffff9286c2714000
[  534.714856] R13: ffffb6d9c0263e08 R14: ffff9286c2714b60 R15: ffff9286c2748050
[  534.715283] FS:  0000000000000000(0000) GS:ffff9286ffc80000(0000) knlGS:0000000000000000
[  534.715761] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  534.716196] CR2: 00007fa6359f00c8 CR3: 0000000002674002 CR4: 00000000001706f0
[  534.716744] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  534.717291] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  534.717691] Call Trace:
[  534.717828]  <TASK>
[  534.717951] ? __warn (kernel/panic.c:677) 
[  534.718150] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  534.718401] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  534.718613] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  534.718816] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  534.719035] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  534.719273] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  534.719527] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  534.719776] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  534.720083] br_dev_delete (net/bridge/br_if.c:396) bridge
[  534.720336] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  534.720628] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  534.720833] ? process_one_work (kernel/workqueue.c:2606) 
[  534.721068] process_one_work (kernel/workqueue.c:2638) 
[  534.721292] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  534.721498] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  534.721734] kthread (kernel/kthread.c:388) 
[  534.721911] ? __pfx_kthread (kernel/kthread.c:341) 
[  534.722123] ret_from_fork (arch/x86/kernel/process.c:153) 
[  534.722326] ? __pfx_kthread (kernel/kthread.c:341) 
[  534.722533] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  534.725169] ------------[ cut here ]------------
| [  534.725420] sysfs group 'bridge' not found for kobject 'br2'
| [  534.725743] WARNING: CPU: 1 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  534.726181] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel sch_ingress em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  534.727415] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  534.728016] Workqueue: netns cleanup_net
[  534.728233] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 534.728497] 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 ba 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 ba 	mov    $0xffffffffba6f0688,%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)
	...
[  534.729479] RSP: 0018:ffffb6d9c0263d70 EFLAGS: 00010286
[  534.729764] RAX: 0000000000000000 RBX: ffffffffc030bc60 RCX: 00000000ffffdfff
[  534.730157] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  534.730535] RBP: 0000000000000000 R08: ffffffffbab64508 R09: 00000000ffffdfff
[  534.730910] R10: ffffffffbaa84520 R11: ffffffffbab34520 R12: ffff9286c27145f8
[  534.731295] R13: ffffb6d9c0263e08 R14: ffff9286c2714b60 R15: ffff9286c2748050
[  534.731674] FS:  0000000000000000(0000) GS:ffff9286ffc80000(0000) knlGS:0000000000000000
[  534.732113] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  534.732423] CR2: 00007fa6359f00c8 CR3: 0000000002674002 CR4: 00000000001706f0
[  534.732804] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  534.733190] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  534.733573] Call Trace:
[  534.733712]  <TASK>
[  534.733833] ? __warn (kernel/panic.c:677) 
[  534.734018] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  534.734249] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  534.734458] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  534.734652] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  534.734868] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  534.735107] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  534.735341] br_dev_delete (net/bridge/br_if.c:396) bridge
[  534.735602] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  534.735894] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  534.736107] ? process_one_work (kernel/workqueue.c:2606) 
[  534.736338] process_one_work (kernel/workqueue.c:2638) 
[  534.736561] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  534.736778] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  534.737017] kthread (kernel/kthread.c:388) 
[  534.737193] ? __pfx_kthread (kernel/kthread.c:341) 
[  534.737410] ret_from_fork (arch/x86/kernel/process.c:153) 
[  534.737611] ? __pfx_kthread (kernel/kthread.c:341) 
[  534.737816] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  534.842134] ------------[ cut here ]------------
| [  534.842392] sysfs group 'bridge' not found for kobject 'br2'
| [  534.842724] WARNING: CPU: 2 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  534.843199] Modules linked in: act_gact cls_flower vxlan ip6_udp_tunnel udp_tunnel sch_ingress em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  534.844739] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  534.845640] Workqueue: netns cleanup_net
[  534.845979] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 534.846367] 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 ba 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 ba 	mov    $0xffffffffba6f0688,%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)
	...
[  534.847915] RSP: 0018:ffffb6d9c0263d70 EFLAGS: 00010286
[  534.848346] RAX: 0000000000000000 RBX: ffffffffc030bc60 RCX: 00000000ffffdfff
[  534.848904] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  534.849478] RBP: 0000000000000000 R08: ffffffffbab64508 R09: 00000000ffffdfff
[  534.850054] R10: ffffffffbaa84520 R11: ffffffffbab34520 R12: ffff9286c190a5f8
[  534.850615] R13: ffffb6d9c0263e08 R14: ffff9286c190ab60 R15: ffffffffbc013dd0
[  534.851188] FS:  0000000000000000(0000) GS:ffff9286ffd00000(0000) knlGS:0000000000000000
[  534.851819] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  534.852288] CR2: 00007f24a88261b4 CR3: 000000003d84c005 CR4: 00000000001706f0
[  534.852858] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  534.853448] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  534.854019] Call Trace:
[  534.854231]  <TASK>
[  534.854409] ? __warn (kernel/panic.c:677) 
[  534.854592] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  534.854824] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  534.855041] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  534.855256] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  534.855467] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  534.855702] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  534.855931] br_dev_delete (net/bridge/br_if.c:396) bridge
[  534.856225] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  534.856517] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  534.856719] ? process_one_work (kernel/workqueue.c:2606) 
[  534.856951] process_one_work (kernel/workqueue.c:2638) 
[  534.857189] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  534.857411] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  534.857647] kthread (kernel/kthread.c:388) 
[  534.857822] ? __pfx_kthread (kernel/kthread.c:341) 
[  534.858034] ret_from_fork (arch/x86/kernel/process.c:153) 
[  534.858243] ? __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