======================================
| [   30.868358] ------------[ cut here ]------------
| [   30.868636] refcount_t: underflow; use-after-free.
| [   30.869002] WARNING: CPU: 1 PID: 11 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [   30.869436] Modules linked in: xfrm_user psample macsec fou vxlan ip6_udp_tunnel udp_tunnel ip6_gre ip_gre gre cls_u32 sch_htb [last unloaded: netdevsim]
[   30.870538] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   30.871149] Workqueue: netns cleanup_net
[   30.871362] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 30.871643] 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 d3 aa 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 d3 aa 	mov    $0xffffffffaad337b8,%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
[   30.872620] RSP: 0018:ffffbd8c40063d78 EFLAGS: 00010286
[   30.872919] RAX: 0000000000000000 RBX: ffff94878233a000 RCX: 00000000ffffdfff
[   30.873289] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   30.873656] RBP: ffff94878233a610 R08: ffffffffab178508 R09: 00000000ffffdfff
[   30.874040] R10: ffffffffab098520 R11: ffffffffab148520 R12: ffff94878233a000
[   30.874407] R13: ffffbd8c40063e08 R14: ffff94878233ab80 R15: ffffffffac678f90
[   30.874787] FS:  0000000000000000(0000) GS:ffff9487bec80000(0000) knlGS:0000000000000000
[   30.875213] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   30.875514] CR2: 000055bf2918edec CR3: 0000000005e5a002 CR4: 0000000000770ef0
[   30.875895] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   30.876261] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   30.876628] PKRU: 55555554
[   30.876780] Call Trace:
[   30.876928]  <TASK>
[   30.877049] ? __warn (kernel/panic.c:677) 
[   30.877225] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   30.877473] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   30.877675] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   30.877882] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   30.878089] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   30.878318] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   30.878563] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[   30.878830] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) 
[   30.879043] br_dev_delete (net/bridge/br_if.c:396) 
[   30.879240] br_net_exit_batch_rtnl (net/bridge/br.c:369) 
[   30.879474] cleanup_net (net/core/net_namespace.c:630) 
[   30.879671] ? process_one_work (kernel/workqueue.c:2606) 
[   30.879914] process_one_work (kernel/workqueue.c:2633) 
[   30.880129] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   30.880329] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   30.880559] kthread (kernel/kthread.c:388) 
[   30.880732] ? __pfx_kthread (kernel/kthread.c:341) 
[   30.880958] ret_from_fork (arch/x86/kernel/process.c:147) 
[   30.881167] ? __pfx_kthread (kernel/kthread.c:341) 
[   30.881472] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [   30.884336] ------------[ cut here ]------------
| [   30.884729] sysfs group 'bridge' not found for kobject 'test-br0'
| [   30.885250] WARNING: CPU: 2 PID: 11 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [   30.885886] Modules linked in: xfrm_user psample macsec fou vxlan ip6_udp_tunnel udp_tunnel ip6_gre ip_gre gre cls_u32 sch_htb [last unloaded: netdevsim]
[   30.887676] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   30.888595] Workqueue: netns cleanup_net
[   30.888947] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 30.889329] 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 d2 aa 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 d2 aa 	mov    $0xffffffffaad2cda0,%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)
	...
[   30.890796] RSP: 0018:ffffbd8c40063d70 EFLAGS: 00010286
[   30.891227] RAX: 0000000000000000 RBX: ffffffffaa9472c0 RCX: 00000000ffffdfff
[   30.891796] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[   30.892355] RBP: 0000000000000000 R08: ffffffffab178508 R09: 00000000ffffdfff
[   30.892918] R10: ffffffffab098520 R11: ffffffffab148520 R12: ffff94878233a610
[   30.893474] R13: ffffbd8c40063e08 R14: ffff94878233ab80 R15: ffffffffac678f90
[   30.894042] FS:  0000000000000000(0000) GS:ffff9487bed00000(0000) knlGS:0000000000000000
[   30.894673] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   30.895147] CR2: 00007f74649e3a30 CR3: 000000001e060003 CR4: 0000000000770ef0
[   30.895715] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   30.896292] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   30.896875] PKRU: 55555554
[   30.897103] Call Trace:
[   30.897312]  <TASK>
[   30.897493] ? __warn (kernel/panic.c:677) 
[   30.897767] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   30.898121] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[   30.898424] ? handle_bug (arch/x86/kernel/traps.c:238) 
[   30.898713] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[   30.899042] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[   30.899375] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[   30.899710] br_dev_delete (net/bridge/br_if.c:396) 
[   30.900022] br_net_exit_batch_rtnl (net/bridge/br.c:369) 
[   30.900384] cleanup_net (net/core/net_namespace.c:630) 
[   30.900678] ? process_one_work (kernel/workqueue.c:2606) 
[   30.901030] process_one_work (kernel/workqueue.c:2633) 
[   30.901348] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[   30.901646] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[   30.902000] kthread (kernel/kthread.c:388) 
[   30.902266] ? __pfx_kthread (kernel/kthread.c:341) 
[   30.902574] ret_from_fork (arch/x86/kernel/process.c:147) 
[   30.902885] ? __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