======================================
| [  790.587421] ------------[ cut here ]------------
| [  790.587702] refcount_t: underflow; use-after-free.
| [  790.588004] WARNING: CPU: 3 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  790.588513] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred ip6_gre ip6_tunnel tunnel6 cls_matchall act_pedit macvlan act_gact cls_flower sch_ingress ip_gre gre em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  790.590124] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  790.590782] Workqueue: netns cleanup_net
[  790.591013] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 790.591318] 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 0f 94 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 0f 94 	mov    $0xffffffff940f70c8,%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
[  790.592300] RSP: 0018:ffffb832c0063d78 EFLAGS: 00010286
[  790.592619] RAX: 0000000000000000 RBX: ffff8d758281a000 RCX: 00000000ffffdfff
[  790.593012] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  790.593419] RBP: ffff8d758281a5f8 R08: ffffffff94564508 R09: 00000000ffffdfff
[  790.593806] R10: ffffffff94484520 R11: ffffffff94534520 R12: ffff8d758281a000
[  790.594185] R13: ffffb832c0063e08 R14: ffff8d758281ab60 R15: ffffffff95a13dd0
[  790.594593] FS:  0000000000000000(0000) GS:ffff8d75bed80000(0000) knlGS:0000000000000000
[  790.595084] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  790.595405] CR2: 00007f7a1e24a1b4 CR3: 000000003624c004 CR4: 00000000001706f0
[  790.595813] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  790.596215] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  790.596644] Call Trace:
[  790.596791]  <TASK>
[  790.596916] ? __warn (kernel/panic.c:677) 
[  790.597104] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  790.597371] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  790.597581] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  790.597775] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  790.597986] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  790.598226] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  790.598487] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  790.598746] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) bridge
[  790.599041] br_dev_delete (net/bridge/br_if.c:396) bridge
[  790.599315] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  790.599608] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  790.599813] ? process_one_work (kernel/workqueue.c:2606) 
[  790.600045] process_one_work (kernel/workqueue.c:2638) 
[  790.600269] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  790.600515] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  790.600761] kthread (kernel/kthread.c:388) 
[  790.600941] ? __pfx_kthread (kernel/kthread.c:341) 
[  790.601147] ret_from_fork (arch/x86/kernel/process.c:153) 
[  790.601358] ? __pfx_kthread (kernel/kthread.c:341) 
[  790.601564] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  790.604228] ------------[ cut here ]------------
| [  790.604522] sysfs group 'bridge' not found for kobject 'br1'
| [  790.604851] WARNING: CPU: 3 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  790.605371] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel act_mirred ip6_gre ip6_tunnel tunnel6 cls_matchall act_pedit macvlan act_gact cls_flower sch_ingress ip_gre gre em_meta cls_basic sch_ets sch_tbf bridge stp llc 8021q vrf veth
[  790.606985] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  790.607594] Workqueue: netns cleanup_net
[  790.607815] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 790.608083] 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 0f 94 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 0f 94 	mov    $0xffffffff940f06b0,%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)
	...
[  790.609129] RSP: 0018:ffffb832c0063d70 EFLAGS: 00010286
[  790.609438] RAX: 0000000000000000 RBX: ffffffffc051dc60 RCX: 00000000ffffdfff
[  790.609825] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  790.610226] RBP: 0000000000000000 R08: ffffffff94564508 R09: 00000000ffffdfff
[  790.610625] R10: ffffffff94484520 R11: ffffffff94534520 R12: ffff8d758281a5f8
[  790.611006] R13: ffffb832c0063e08 R14: ffff8d758281ab60 R15: ffffffff95a13dd0
[  790.611412] FS:  0000000000000000(0000) GS:ffff8d75bed80000(0000) knlGS:0000000000000000
[  790.611875] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  790.612197] CR2: 00007f7a1e24a1b4 CR3: 000000003624c004 CR4: 00000000001706f0
[  790.612639] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  790.613076] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  790.613475] Call Trace:
[  790.613617]  <TASK>
[  790.613740] ? __warn (kernel/panic.c:677) 
[  790.613923] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  790.614176] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  790.614393] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  790.614593] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  790.614808] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  790.615056] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  790.615315] br_dev_delete (net/bridge/br_if.c:396) bridge
[  790.615591] br_net_exit_batch_rtnl (net/bridge/br.c:369) bridge
[  790.615889] cleanup_net (net/core/net_namespace.c:628 (discriminator 2)) 
[  790.616100] ? process_one_work (kernel/workqueue.c:2606) 
[  790.616351] process_one_work (kernel/workqueue.c:2638) 
[  790.616596] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  790.616831] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  790.617080] kthread (kernel/kthread.c:388) 
[  790.617266] ? __pfx_kthread (kernel/kthread.c:341) 
[  790.617504] ret_from_fork (arch/x86/kernel/process.c:153) 
[  790.617707] ? __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