======================================
| [ 1357.390222] ------------[ cut here ]------------
| [ 1357.390509] refcount_t: underflow; use-after-free.
| [ 1357.390875] WARNING: CPU: 3 PID: 67 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [ 1357.391322] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_skbedit sch_prio sch_tbf act_mirred cls_matchall dummy bridge stp llc ip_gre act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[ 1357.392875] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1357.393529] Workqueue: netns cleanup_net
[ 1357.393783] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1357.394092] 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 2f b0 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 2f b0 	mov    $0xffffffffb02f70a0,%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
[ 1357.395202] RSP: 0018:ffffb074c025bd78 EFLAGS: 00010286
[ 1357.395510] RAX: 0000000000000000 RBX: ffffa053c66e6000 RCX: 00000000ffffdfff
[ 1357.395949] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1357.396349] RBP: ffffa053c66e65f8 R08: ffffffffb0764508 R09: 00000000ffffdfff
[ 1357.396743] R10: ffffffffb0684520 R11: ffffffffb0734520 R12: ffffa053c66e6000
[ 1357.397131] R13: ffffb074c025be08 R14: ffffa053c66e6b60 R15: ffffa053c47e0050
[ 1357.397518] FS:  0000000000000000(0000) GS:ffffa053fed80000(0000) knlGS:0000000000000000
[ 1357.397984] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1357.398307] CR2: 00007f3406532270 CR3: 000000002b84c001 CR4: 00000000001706f0
[ 1357.398746] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1357.399136] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1357.399515] Call Trace:
[ 1357.399664]  <TASK>
[ 1357.399789] ? __warn (kernel/panic.c:677) 
[ 1357.400007] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1357.400262] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1357.400493] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1357.400720] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1357.400956] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1357.401210] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1357.401480] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 1357.401768] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[ 1357.402088] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1357.402361] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1357.402729] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1357.402943] ? process_one_work (kernel/workqueue.c:2606) 
[ 1357.403190] process_one_work (kernel/workqueue.c:2638) 
[ 1357.403430] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1357.403668] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1357.403928] kthread (kernel/kthread.c:388) 
[ 1357.404106] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1357.404329] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1357.404566] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1357.404795] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1357.407673] ------------[ cut here ]------------
| [ 1357.407955] sysfs group 'bridge' not found for kobject 'br3'
| [ 1357.408328] WARNING: CPU: 3 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1357.408783] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_skbedit sch_prio sch_tbf act_mirred cls_matchall dummy bridge stp llc ip_gre act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[ 1357.410421] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1357.411114] Workqueue: netns cleanup_net
[ 1357.411349] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1357.411634] 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 2f b0 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 2f b0 	mov    $0xffffffffb02f0688,%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)
	...
[ 1357.412646] RSP: 0018:ffffb074c025bd70 EFLAGS: 00010286
[ 1357.412938] RAX: 0000000000000000 RBX: ffffffffc03ecc60 RCX: 00000000ffffdfff
[ 1357.413324] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1357.413718] RBP: 0000000000000000 R08: ffffffffb0764508 R09: 00000000ffffdfff
[ 1357.414113] R10: ffffffffb0684520 R11: ffffffffb0734520 R12: ffffa053c66e65f8
[ 1357.414494] R13: ffffb074c025be08 R14: ffffa053c66e6b60 R15: ffffa053c47e0050
[ 1357.414958] FS:  0000000000000000(0000) GS:ffffa053fed80000(0000) knlGS:0000000000000000
[ 1357.415392] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1357.415712] CR2: 00007f3406532270 CR3: 000000002b84c001 CR4: 00000000001706f0
[ 1357.416101] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1357.416506] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1357.416928] Call Trace:
[ 1357.417083]  <TASK>
[ 1357.417211] ? __warn (kernel/panic.c:677) 
[ 1357.417411] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1357.417673] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1357.417907] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1357.418123] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1357.418355] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1357.418630] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1357.418921] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1357.419184] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1357.419477] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1357.419722] ? process_one_work (kernel/workqueue.c:2606) 
[ 1357.419979] process_one_work (kernel/workqueue.c:2638) 
[ 1357.420232] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1357.420459] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1357.420730] kthread (kernel/kthread.c:388) 
[ 1357.420924] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1357.421144] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1357.421363] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1357.421602] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [ 1357.551091] ------------[ cut here ]------------
| [ 1357.551379] sysfs group 'bridge' not found for kobject 'br3'
| [ 1357.551709] WARNING: CPU: 3 PID: 67 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [ 1357.552176] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_skbedit sch_prio sch_tbf act_mirred cls_matchall dummy bridge stp llc ip_gre act_gact cls_flower sch_ingress 8021q ip6_gre ip6_tunnel tunnel6 gre vrf veth
[ 1357.553733] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1357.554353] Workqueue: netns cleanup_net
[ 1357.554576] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1357.554846] 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 2f b0 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 2f b0 	mov    $0xffffffffb02f0688,%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)
	...
[ 1357.555830] RSP: 0018:ffffb074c025bd70 EFLAGS: 00010286
[ 1357.556125] RAX: 0000000000000000 RBX: ffffffffc03ecc60 RCX: 00000000ffffdfff
[ 1357.556506] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 1357.556895] RBP: 0000000000000000 R08: ffffffffb0764508 R09: 00000000ffffdfff
[ 1357.557278] R10: ffffffffb0684520 R11: ffffffffb0734520 R12: ffffa053c24505f8
[ 1357.557673] R13: ffffb074c025be08 R14: ffffa053c2450b60 R15: ffffffffb1c13dd0
[ 1357.558071] FS:  0000000000000000(0000) GS:ffffa053fed80000(0000) knlGS:0000000000000000
[ 1357.558504] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1357.558813] CR2: 00007f0d2a39b000 CR3: 000000002b84c001 CR4: 00000000001706f0
[ 1357.559206] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1357.559591] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1357.559984] Call Trace:
[ 1357.560127]  <TASK>
[ 1357.560252] ? __warn (kernel/panic.c:677) 
[ 1357.560434] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1357.560669] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[ 1357.560886] ? handle_bug (arch/x86/kernel/traps.c:238) 
[ 1357.561085] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[ 1357.561304] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[ 1357.561564] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 1357.561864] br_dev_delete (net/bridge/br_if.c:396) bridge
[ 1357.562225] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[ 1357.562537] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[ 1357.562814] ? process_one_work (kernel/workqueue.c:2606) 
[ 1357.563101] process_one_work (kernel/workqueue.c:2638) 
[ 1357.563389] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[ 1357.563676] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[ 1357.564011] kthread (kernel/kthread.c:388) 
[ 1357.564254] ? __pfx_kthread (kernel/kthread.c:341) 
[ 1357.564543] ret_from_fork (arch/x86/kernel/process.c:153) 
[ 1357.564825] ? __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