======================================
| [  139.593094] ------------[ cut here ]------------
| [  139.593611] refcount_t: underflow; use-after-free.
| [  139.594068] WARNING: CPU: 3 PID: 69 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  139.594933] Modules linked in: xt_length nft_compat nf_tables act_ct nf_flow_table nf_nat nf_conntrack libcrc32c nf_defrag_ipv6 nf_defrag_ipv4 cls_flower sch_ingress
[  139.596280] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  139.596873] Workqueue: netns cleanup_net
[  139.597082] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 139.597364] Code: 0b 90 90 c3 cc cc cc cc 80 3d 69 d4 67 01 00 0f 85 75 ff ff ff c6 05 5c d4 67 01 01 90 48 c7 c7 b8 37 13 8c e8 a1 26 b4 ff 90 <0f> 0b 90 90 c3 cc cc cc cc 80 3d 3c d4 67 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 69 d4 67 01 00 	cmpb   $0x0,0x167d469(%rip)        # 0x167d478
   f:	0f 85 75 ff ff ff    	jne    0xffffffffffffff8a
  15:	c6 05 5c d4 67 01 01 	movb   $0x1,0x167d45c(%rip)        # 0x167d478
  1c:	90                   	nop
  1d:	48 c7 c7 b8 37 13 8c 	mov    $0xffffffff8c1337b8,%rdi
  24:	e8 a1 26 b4 ff       	call   0xffffffffffb426ca
  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 3c d4 67 01 00 	cmpb   $0x0,0x167d43c(%rip)        # 0x167d476
  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 3c d4 67 01 00 	cmpb   $0x0,0x167d43c(%rip)        # 0x167d44c
  10:	0f 85 4a ff ff ff    	jne    0xffffffffffffff60
[  139.598325] RSP: 0018:ffffa14c8026bd78 EFLAGS: 00010286
[  139.598610] RAX: 0000000000000000 RBX: ffff8c2e83560000 RCX: 00000000ffffdfff
[  139.599041] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  139.599405] RBP: ffff8c2e83560610 R08: ffffffff8c578508 R09: 00000000ffffdfff
[  139.599999] R10: ffffffff8c498520 R11: ffffffff8c548520 R12: ffff8c2e83560000
[  139.600363] R13: ffffa14c8026be08 R14: ffff8c2e83560b80 R15: ffff8c2e82765c50
[  139.600724] FS:  0000000000000000(0000) GS:ffff8c2ebed80000(0000) knlGS:0000000000000000
[  139.601150] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  139.601447] CR2: 00007f30a26c6270 CR3: 000000001aa60005 CR4: 0000000000770ef0
[  139.601817] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  139.602181] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  139.602550] PKRU: 55555554
[  139.602696] Call Trace:
[  139.602841]  <TASK>
[  139.602967] ? __warn (kernel/panic.c:677) 
[  139.603141] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  139.603387] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  139.603588] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  139.603774] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  139.603983] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  139.604214] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  139.604461] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  139.604706] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) 
[  139.604914] br_dev_delete (net/bridge/br_if.c:396) 
[  139.605113] br_net_exit_batch_rtnl (net/bridge/br.c:369) 
[  139.605349] cleanup_net (net/core/net_namespace.c:630) 
[  139.605543] ? process_one_work (kernel/workqueue.c:2606) 
[  139.605768] process_one_work (kernel/workqueue.c:2633) 
[  139.606008] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  139.606244] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  139.606548] kthread (kernel/kthread.c:388) 
[  139.606778] ? __pfx_kthread (kernel/kthread.c:341) 
[  139.607061] ret_from_fork (arch/x86/kernel/process.c:147) 
[  139.607327] ? __pfx_kthread (kernel/kthread.c:341) 
[  139.607602] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  139.611082] ------------[ cut here ]------------
| [  139.611388] sysfs group 'bridge' not found for kobject 'br0'
| [  139.611907] WARNING: CPU: 3 PID: 69 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  139.612330] Modules linked in: xt_length nft_compat nf_tables act_ct nf_flow_table nf_nat nf_conntrack libcrc32c nf_defrag_ipv6 nf_defrag_ipv4 cls_flower sch_ingress
[  139.614792] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  139.615638] Workqueue: netns cleanup_net
[  139.616090] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 139.616613] Code: 48 89 ef 5d 41 5c e9 7a ad ff ff 48 89 ef e8 12 9b ff ff eb d1 90 49 8b 14 24 48 8b 33 48 c7 c7 a0 cd 12 8c e8 ac 67 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 7a ad ff ff       	jmp    0xffffffffffffad85
   b:	48 89 ef             	mov    %rbp,%rdi
   e:	e8 12 9b ff ff       	call   0xffffffffffff9b25
  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 a0 cd 12 8c 	mov    $0xffffffff8c12cda0,%rdi
  24:	e8 ac 67 c5 ff       	call   0xffffffffffc567d5
  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)
	...
[  139.618680] RSP: 0018:ffffa14c8026bd70 EFLAGS: 00010286
[  139.619292] RAX: 0000000000000000 RBX: ffffffff8bd472c0 RCX: 00000000ffffdfff
[  139.620056] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  139.620925] RBP: 0000000000000000 R08: ffffffff8c578508 R09: 00000000ffffdfff
[  139.621782] R10: ffffffff8c498520 R11: ffffffff8c548520 R12: ffff8c2e83560610
[  139.622261] R13: ffffa14c8026be08 R14: ffff8c2e83560b80 R15: ffff8c2e82765c50
[  139.622709] FS:  0000000000000000(0000) GS:ffff8c2ebed80000(0000) knlGS:0000000000000000
[  139.623140] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  139.623544] CR2: 00007f30a26c6270 CR3: 000000001aa60005 CR4: 0000000000770ef0
[  139.624170] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  139.624681] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  139.625401] PKRU: 55555554
[  139.625746] Call Trace:
[  139.626035]  <TASK>
[  139.626286] ? __warn (kernel/panic.c:677) 
[  139.626689] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  139.627204] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  139.627667] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  139.628110] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  139.628497] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  139.628922] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  139.629331] br_dev_delete (net/bridge/br_if.c:396) 
[  139.629694] br_net_exit_batch_rtnl (net/bridge/br.c:369) 
[  139.630115] cleanup_net (net/core/net_namespace.c:630) 
[  139.630440] ? process_one_work (kernel/workqueue.c:2606) 
[  139.630861] process_one_work (kernel/workqueue.c:2633) 
[  139.631181] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  139.631492] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  139.631867] kthread (kernel/kthread.c:388) 
[  139.632127] ? __pfx_kthread (kernel/kthread.c:341) 
[  139.632451] ret_from_fork (arch/x86/kernel/process.c:147) 
[  139.632772] ? __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