I started seeing this too after upgrading to this kernel (from https://ubuntu.com/security/notices/USN-6081-1):

ii  linux-image-generic                    4.15.0.211.194
ii  linux-image-4.15.0-211-generic         4.15.0-211.222

$ cat /proc/version_signature 
Ubuntu 4.15.0-211.222-generic 4.15.18

From /var/log/syslog:
May 27 15:18:43 <hostname> kernel: [22004.663374] ------------[ cut here ]------------
May 27 15:18:43 <hostname> kernel: [22004.663397] WARNING: CPU: 6 PID: 0 at /build/linux-RlFMDZ/linux-4.15.0/net/core/stream.c:212 sk_stream_kill_queues+0xed/0x110
May 27 15:18:43 <hostname> kernel: [22004.663398] Modules linked in: dm_crypt algif_skcipher af_alg nls_iso8859_1 ip6t_REJECT nf_reject_ipv6 nf_log_ipv6 xt_hl ip6t_rt nf_conntrack_ipv6 nf_defrag_ipv6 xt_comment ipt_REJECT nf_reject_ipv4 nf_log_ipv4 nf_log_common xt_LOG xt_recent ipt_MASQUERADE nf_nat_masquerade_ipv4 xt_nat intel_rapl ipmi_ssif x86_pkg_temp_thermal intel_powerclamp binfmt_misc kvm_intel kvm irqbypass dcdbas mgag200 iptable_nat ttm nf_nat_ipv4 crct10dif_pclmul xt_limit crc32_pclmul drm_kms_helper xt_tcpudp ghash_clmulni_intel pcbc drm xt_addrtype i2c_algo_bit aesni_intel aes_x86_64 crypto_simd glue_helper cryptd fb_sys_fops syscopyarea intel_cstate sysfillrect intel_rapl_perf sysimgblt lpc_ich shpchp ie31200_edac ipmi_si ipmi_devintf wmi ipmi_msghandler mac_hid nf_conntrack_ipv4 nf_defrag_ipv4 sch_fq_codel xt_conntrack
May 27 15:18:43 <hostname> kernel: [22004.663428]  ip6table_filter ip6_tables nf_conntrack_netbios_ns nf_conntrack_broadcast nf_nat_ftp nf_nat nf_conntrack_ftp nf_conntrack iptable_filter coretemp lp parport ip_tables x_tables autofs4 raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid0 multipath linear raid1 tg3 ahci ptp libahci pps_core
May 27 15:18:43 <hostname> kernel: [22004.663444] CPU: 6 PID: 0 Comm: swapper/6 Tainted: G        W        4.15.0-211-generic #222-Ubuntu
May 27 15:18:43 <hostname> kernel: [22004.663446] Hardware name: Dell Inc. PowerEdge T110 II/0PM2CW, BIOS 2.8.0 06/24/2014
May 27 15:18:43 <hostname> kernel: [22004.663449] RIP: 0010:sk_stream_kill_queues+0xed/0x110
May 27 15:18:43 <hostname> kernel: [22004.663450] RSP: 0018:ffff99813fd83920 EFLAGS: 00010282
May 27 15:18:43 <hostname> kernel: [22004.663452] RAX: 0000000000000024 RBX: ffff997fb1479980 RCX: 0000000000000006
May 27 15:18:43 <hostname> kernel: [22004.663453] RDX: 0000000000000000 RSI: ffff99813fd9b4d8 RDI: ffff99813fd9b4d0
May 27 15:18:43 <hostname> kernel: [22004.663454] RBP: ffff99813fd83930 R08: 0000000000007b7b R09: 0000000000000004
May 27 15:18:43 <hostname> kernel: [22004.663456] R10: ffff99813fd83958 R11: 0000000000000001 R12: ffff997fb1479a48
May 27 15:18:43 <hostname> kernel: [22004.663457] R13: 0000000000000006 R14: 000000000000003c R15: 0000000000000000
May 27 15:18:43 <hostname> kernel: [22004.663459] FS:  0000000000000000(0000) GS:ffff99813fd80000(0000) knlGS:0000000000000000
May 27 15:18:43 <hostname> kernel: [22004.663460] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
May 27 15:18:43 <hostname> kernel: [22004.663461] CR2: 0000563185766000 CR3: 000000027d40a001 CR4: 00000000001606e0
May 27 15:18:43 <hostname> kernel: [22004.663462] Call Trace:
May 27 15:18:43 <hostname> kernel: [22004.663465]  <IRQ>
May 27 15:18:43 <hostname> kernel: [22004.663472]  inet_csk_destroy_sock+0x59/0x150
May 27 15:18:43 <hostname> kernel: [22004.663474]  tcp_done+0x96/0xa0
May 27 15:18:43 <hostname> kernel: [22004.663476]  tcp_time_wait+0x1be/0x280
May 27 15:18:43 <hostname> kernel: [22004.663479]  tcp_fin+0x16b/0x180
May 27 15:18:43 <hostname> kernel: [22004.663481]  tcp_data_queue+0x594/0xc20
May 27 15:18:43 <hostname> kernel: [22004.663484]  tcp_rcv_state_process+0x5dd/0xe70
May 27 15:18:43 <hostname> kernel: [22004.663486]  ? skb_clone+0x56/0xc0
May 27 15:18:43 <hostname> kernel: [22004.663490]  tcp_v6_do_rcv+0x1ca/0x440
May 27 15:18:43 <hostname> kernel: [22004.663492]  ? tcp_v6_do_rcv+0x1ca/0x440
May 27 15:18:43 <hostname> kernel: [22004.663494]  tcp_v6_rcv+0x9b6/0xa60
May 27 15:18:43 <hostname> kernel: [22004.663503]  ? nf_ct_get_tuple+0x82/0xa0 [nf_conntrack]
May 27 15:18:43 <hostname> kernel: [22004.663507]  ip6_input_finish+0xcc/0x470
May 27 15:18:43 <hostname> kernel: [22004.663509]  ip6_input+0x3f/0xb0
May 27 15:18:43 <hostname> kernel: [22004.663511]  ? ipv6_is_mld+0xa0/0xa0
May 27 15:18:43 <hostname> kernel: [22004.663513]  ip6_rcv_finish+0xd8/0x120
May 27 15:18:43 <hostname> kernel: [22004.663514]  ipv6_rcv+0x347/0x510
May 27 15:18:43 <hostname> kernel: [22004.663516]  ? ip6_make_skb+0x200/0x200
May 27 15:18:43 <hostname> kernel: [22004.663520]  __netif_receive_skb_core+0x432/0xb80
May 27 15:18:43 <hostname> kernel: [22004.663524]  ? tcp6_gro_receive+0x137/0x1a0
May 27 15:18:43 <hostname> kernel: [22004.663527]  ? ipv6_gro_receive+0x1a6/0x350
May 27 15:18:43 <hostname> kernel: [22004.663529]  __netif_receive_skb+0x18/0x60
May 27 15:18:43 <hostname> kernel: [22004.663531]  ? __netif_receive_skb+0x18/0x60
May 27 15:18:43 <hostname> kernel: [22004.663534]  netif_receive_skb_internal+0x45/0xe0
May 27 15:18:43 <hostname> kernel: [22004.663537]  napi_gro_receive+0xc5/0xf0
May 27 15:18:43 <hostname> kernel: [22004.663542]  tg3_poll_work+0x3b2/0xf10 [tg3]
May 27 15:18:43 <hostname> kernel: [22004.663548]  tg3_poll+0x6b/0x3a0 [tg3]
May 27 15:18:43 <hostname> kernel: [22004.663550]  net_rx_action+0x140/0x3d0
May 27 15:18:43 <hostname> kernel: [22004.663556]  __do_softirq+0xe4/0x2d4
May 27 15:18:43 <hostname> kernel: [22004.663559]  irq_exit+0xc5/0xd0
May 27 15:18:43 <hostname> kernel: [22004.663562]  do_IRQ+0x86/0xe0
May 27 15:18:43 <hostname> kernel: [22004.663564]  common_interrupt+0x90/0x90
May 27 15:18:43 <hostname> kernel: [22004.663565]  </IRQ>
May 27 15:18:43 <hostname> kernel: [22004.663568] RIP: 0010:cpuidle_enter_state+0xa7/0x2f0
May 27 15:18:43 <hostname> kernel: [22004.663569] RSP: 0018:ffffa697c1947e68 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffdc
May 27 15:18:43 <hostname> kernel: [22004.663571] RAX: ffff99813fda69c0 RBX: 000014035c241b5c RCX: 000000000000001f
May 27 15:18:43 <hostname> kernel: [22004.663572] RDX: 000014035c241b5c RSI: ffffffef2d8e461a RDI: 0000000000000000
May 27 15:18:43 <hostname> kernel: [22004.663574] RBP: ffffa697c1947ea8 R08: 0000000000000004 R09: 0000000000026200
May 27 15:18:43 <hostname> kernel: [22004.663575] R10: ffffa697c1947e38 R11: 0000421c1d2b47a9 R12: ffff99813fdb0900
May 27 15:18:43 <hostname> kernel: [22004.663576] R13: 0000000000000004 R14: ffffffffbf7735d8 R15: 0000000000000000
May 27 15:18:43 <hostname> kernel: [22004.663579]  ? cpuidle_enter_state+0x97/0x2f0
May 27 15:18:43 <hostname> kernel: [22004.663581]  cpuidle_enter+0x17/0x20
May 27 15:18:43 <hostname> kernel: [22004.663584]  call_cpuidle+0x23/0x40
May 27 15:18:43 <hostname> kernel: [22004.663587]  do_idle+0x18c/0x1f0
May 27 15:18:43 <hostname> kernel: [22004.663590]  cpu_startup_entry+0x73/0x80
May 27 15:18:43 <hostname> kernel: [22004.663594]  start_secondary+0x1ab/0x200
May 27 15:18:43 <hostname> kernel: [22004.663597]  secondary_startup_64+0xa5/0xb0
May 27 15:18:43 <hostname> kernel: [22004.663599] Code: 01 00 00 85 d2 74 df 48 c7 c7 f8 62 2b bf e8 50 49 15 00 0f 0b 8b 83 f8 00 00 00 85 c0 74 d1 48 c7 c7 f8 62 2b bf e8 38 49 15 00 <0f> 0b 5b 41 5c 5d c3 48 c7 c7 f8 62 2b bf e8 25 49 15 00 0f 0b 
May 27 15:18:43 <hostname> kernel: [22004.663623] ---[ end trace 9048473a62d7540d ]---