======================================
| [  219.042563] ------------[ cut here ]------------
| [  219.042928] refcount_t: underflow; use-after-free.
| [  219.043209] WARNING: CPU: 1 PID: 68 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
| [  219.043638] Modules linked in: xfrm_interface sha1_generic xfrm_user act_mirred cls_matchall ip6_gre gre nft_chain_nat xt_nat nf_nat vxlan xt_conntrack nf_conntrack nf_defrag_ipv4 nft_compat nf_tables nf_defrag_ipv6 sctp_diag sctp ip6_udp_tunnel udp_tunnel libcrc32c drop_monitor act_gact cls_flower sch_ingress netdevsim psample
[  219.045584] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  219.046400] Workqueue: netns cleanup_net
[  219.046715] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[ 219.046995] 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 e8 37 93 96 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 e8 37 93 96 	mov    $0xffffffff969337e8,%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
[  219.048381] RSP: 0018:ffffb7bdc0263d78 EFLAGS: 00010286
[  219.048844] RAX: 0000000000000000 RBX: ffff9a05839ae000 RCX: 00000000ffffdfff
[  219.049452] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  219.050258] RBP: ffff9a05839ae610 R08: ffffffff96d78508 R09: 00000000ffffdfff
[  219.050913] R10: ffffffff96c98520 R11: ffffffff96d48520 R12: ffff9a05839ae000
[  219.051560] R13: ffffb7bdc0263e08 R14: ffff9a05839aeb80 R15: ffff9a0582bc5c50
[  219.052223] FS:  0000000000000000(0000) GS:ffff9a05bec80000(0000) knlGS:0000000000000000
[  219.052962] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  219.053526] CR2: 000055b01eb77dec CR3: 000000001fa60002 CR4: 0000000000770ef0
[  219.054175] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  219.054542] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  219.054971] PKRU: 55555554
[  219.055117] Call Trace:
[  219.055252]  <TASK>
[  219.055372] ? __warn (kernel/panic.c:677) 
[  219.055551] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  219.055798] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  219.056037] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  219.056319] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  219.056652] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  219.056882] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  219.057256] ? refcount_warn_saturate (lib/refcount.c:28 (discriminator 3)) 
[  219.057685] br_sysfs_delbr (net/bridge/br_sysfs_br.c:1086) 
[  219.058057] br_dev_delete (net/bridge/br_if.c:396) 
[  219.058424] br_net_exit_batch_rtnl (net/bridge/br.c:369) 
[  219.058868] cleanup_net (net/core/net_namespace.c:630) 
[  219.059238] ? process_one_work (kernel/workqueue.c:2606) 
[  219.059686] process_one_work (kernel/workqueue.c:2633) 
[  219.060097] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  219.060479] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  219.060946] kthread (kernel/kthread.c:388) 
[  219.061367] ? __pfx_kthread (kernel/kthread.c:341) 
[  219.061838] ret_from_fork (arch/x86/kernel/process.c:147) 
[  219.062294] ? __pfx_kthread (kernel/kthread.c:341) 
[  219.062762] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  219.067027] ------------[ cut here ]------------
| [  219.067351] sysfs group 'bridge' not found for kobject 'br0'
| [  219.067666] WARNING: CPU: 3 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  219.068169] Modules linked in: xfrm_interface sha1_generic xfrm_user act_mirred cls_matchall ip6_gre gre nft_chain_nat xt_nat nf_nat vxlan xt_conntrack nf_conntrack nf_defrag_ipv4 nft_compat nf_tables nf_defrag_ipv6 sctp_diag sctp ip6_udp_tunnel udp_tunnel libcrc32c drop_monitor act_gact cls_flower sch_ingress netdevsim psample
[  219.070473] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  219.071057] Workqueue: netns cleanup_net
[  219.071287] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 219.071548] 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 d0 cd 92 96 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 d0 cd 92 96 	mov    $0xffffffff9692cdd0,%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)
	...
[  219.072483] RSP: 0018:ffffb7bdc0263d70 EFLAGS: 00010286
[  219.072753] RAX: 0000000000000000 RBX: ffffffff965472c0 RCX: 00000000ffffdfff
[  219.073140] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  219.073502] RBP: 0000000000000000 R08: ffffffff96d78508 R09: 00000000ffffdfff
[  219.073937] R10: ffffffff96c98520 R11: ffffffff96d48520 R12: ffff9a05839ae610
[  219.074438] R13: ffffb7bdc0263e08 R14: ffff9a05839aeb80 R15: ffff9a0582bc5c50
[  219.074940] FS:  0000000000000000(0000) GS:ffff9a05bed80000(0000) knlGS:0000000000000000
[  219.075788] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  219.076364] CR2: 000055b01eb77dec CR3: 000000001fa60005 CR4: 0000000000770ef0
[  219.077013] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  219.077640] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  219.078285] PKRU: 55555554
[  219.078570] Call Trace:
[  219.078846]  <TASK>
[  219.079053] ? __warn (kernel/panic.c:677) 
[  219.079404] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  219.079826] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  219.080163] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  219.080501] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  219.080893] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  219.081270] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  219.081635] br_dev_delete (net/bridge/br_if.c:396) 
[  219.081929] br_net_exit_batch_rtnl (net/bridge/br.c:369) 
[  219.082325] cleanup_net (net/core/net_namespace.c:630) 
[  219.082674] ? process_one_work (kernel/workqueue.c:2606) 
[  219.083048] process_one_work (kernel/workqueue.c:2633) 
[  219.083425] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  219.083775] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  219.084114] kthread (kernel/kthread.c:388) 
[  219.084390] ? __pfx_kthread (kernel/kthread.c:341) 
[  219.084693] ret_from_fork (arch/x86/kernel/process.c:147) 
[  219.085032] ? __pfx_kthread (kernel/kthread.c:341) 
[  219.085232] ret_from_fork_asm (arch/x86/entry/entry_64.S:250) 
| [  219.195117] ------------[ cut here ]------------
| [  219.195514] sysfs group 'bridge' not found for kobject 'br0'
| [  219.196032] WARNING: CPU: 3 PID: 68 at fs/sysfs/group.c:282 sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
| [  219.196678] Modules linked in: xfrm_interface sha1_generic xfrm_user act_mirred cls_matchall ip6_gre gre nft_chain_nat xt_nat nf_nat vxlan xt_conntrack nf_conntrack nf_defrag_ipv4 nft_compat nf_tables nf_defrag_ipv6 sctp_diag sctp ip6_udp_tunnel udp_tunnel libcrc32c drop_monitor act_gact cls_flower sch_ingress netdevsim psample
[  219.199706] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  219.200607] Workqueue: netns cleanup_net
[  219.200945] RIP: 0010:sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[ 219.201330] 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 d0 cd 92 96 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 d0 cd 92 96 	mov    $0xffffffff9692cdd0,%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)
	...
[  219.202795] RSP: 0018:ffffb7bdc0263d70 EFLAGS: 00010286
[  219.203216] RAX: 0000000000000000 RBX: ffffffff965472c0 RCX: 00000000ffffdfff
[  219.203770] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[  219.204349] RBP: 0000000000000000 R08: ffffffff96d78508 R09: 00000000ffffdfff
[  219.204918] R10: ffffffff96c98520 R11: ffffffff96d48520 R12: ffff9a059193c610
[  219.205476] R13: ffffb7bdc0263e08 R14: ffff9a059193cb80 R15: ffff9a0582bc0050
[  219.206050] FS:  0000000000000000(0000) GS:ffff9a05bed80000(0000) knlGS:0000000000000000
[  219.206685] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  219.207148] CR2: 00007f3a2f63b0e0 CR3: 000000001fa60006 CR4: 0000000000770ef0
[  219.207738] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  219.208315] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  219.208894] PKRU: 55555554
[  219.209115] Call Trace:
[  219.209319]  <TASK>
[  219.209501] ? __warn (kernel/panic.c:677) 
[  219.209782] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  219.210136] ? report_bug (lib/bug.c:201 lib/bug.c:219) 
[  219.210441] ? handle_bug (arch/x86/kernel/traps.c:238) 
[  219.210727] ? exc_invalid_op (arch/x86/kernel/traps.c:259 (discriminator 1)) 
[  219.211049] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:568) 
[  219.211393] ? sysfs_remove_group (fs/sysfs/group.c:282 (discriminator 1)) 
[  219.211747] br_dev_delete (net/bridge/br_if.c:396) 
[  219.212075] br_net_exit_batch_rtnl (net/bridge/br.c:369) 
[  219.212471] cleanup_net (net/core/net_namespace.c:630) 
[  219.212769] ? process_one_work (kernel/workqueue.c:2606) 

[  219.213126] process_one_work (kernel/workqueue.c:2633) 
[  219.213499] worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) 
[  219.213805] ? __pfx_worker_thread (kernel/workqueue.c:2733) 
[  219.214228] kthread (kernel/kthread.c:388) 
[  219.214492] ? __pfx_kthread (kernel/kthread.c:341) 
[  219.214796] ret_from_fork (arch/x86/kernel/process.c:147) 
xx__-> [  219.215157] ? __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