[FS#764] MT6721: Any traffic shaping results in crashes/stack traces

[LEDE Bugs]

The following task has a new comment added:

FS#764 - MT6721: Any traffic shaping results in crashes/stack traces
User who did this - Bartvz (Bartvz)

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Possibly related, if running SQM QoS the following stack traces appear in the kernel and system logs:

Kernel log:
[81578.960000] ------------[ cut here ]------------
[81578.970000] WARNING: CPU: 2 PID: 0 at net/core/skbuff.c:4196 skb_try_coalesce+0x228/0x35c()
[81578.990000] Modules linked in: pppoe ppp_async pppox ppp_generic nf_conntrack_ipv6 iptable_nat ipt_REJECT ipt_MASQUERADE xt_time xt_tcpudp xt_tcpmss xt_statistic xt_state xt_recent xt_nat xt_multiport xt_mark xt_mac xt_limit xt_length xt_hl xt_helper xt_ecn xt_dscp xt_conntrack xt_connmark xt_connlimit xt_connbytes xt_comment xt_TEE xt_TCPMSS xt_REDIRECT xt_LOG xt_HL xt_DSCP xt_CLASSIFY slhc nf_reject_ipv4 nf_nat_redirect nf_nat_masquerade_ipv4 nf_conntrack_ipv4 nf_nat_ipv4 nf_nat nf_log_ipv4 nf_dup_ipv6 nf_dup_ipv4 nf_defrag_ipv6 nf_defrag_ipv4 nf_conntrack_rtcache iptable_mangle iptable_filter ipt_ECN ip_tables crc_ccitt sch_cake nf_conntrack act_skbedit act_mirred em_u32 cls_u32 cls_tcindex cls_flow cls_route cls_fw sch_tbf sch_htb sch_hfsc sch_ingress mt76x2e mt7603e ledtrig_usbport mt76 mac80211 cfg80211 compat xt_set ip_set_list_set ip_set_hash_netiface ip_set_hash_netport ip_set_hash_netnet ip_set_hash_net ip_set_hash_netportnet ip_set_hash_mac ip_set_hash_ipportnet ip_set_hash_ipportip ip_set_hash_ipport ip_set_hash_ipmark ip_set_hash_ip ip_set_bitmap_port ip_set_bitmap_ipmac ip_set_bitmap_ip ip_set nfnetlink ip6t_REJECT nf_reject_ipv6 nf_log_ipv6 nf_log_common ip6table_mangle ip6table_filter ip6_tables x_tables ifb leds_gpio xhci_mtk xhci_plat_hcd xhci_pci xhci_hcd gpio_button_hotplug usbcore nls_base usb_common
[81579.220000] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.4.61 #0
[81579.230000] Stack : 00000000 00000000 804c6862 00000033 00000000 00000000 80470000 804e0000
[81579.230000] 	  87c4b9ec 80465c83 803e352c 00000002 00000000 804c367c 87c1dd3f 804fade0
[81579.230000] 	  00000000 80063258 80470000 804e0000 8046a188 8046a18c 803e8160 87c1dbec
[81579.230000] 	  00000003 80061014 87c1dd3f 804fade0 00000000 00000125 00000000 00c1dbec
[81579.230000] 	  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[81579.230000] 	  ...
[81579.300000] Call Trace:
[81579.310000] [] show_stack+0x6c/0x88
[81579.320000] [] dump_stack+0x8c/0xc0
[81579.330000] [] warn_slowpath_common+0xa0/0xd0
[81579.340000] [] warn_slowpath_null+0x18/0x24
[81579.350000] [] skb_try_coalesce+0x228/0x35c
[81579.360000] [] tcp_try_coalesce+0x70/0xd4
[81579.370000] 
[81579.370000] ---[ end trace 2800734bc845e5bf ]---

System log:
Sat May  6 14:11:36 2017 authpriv.info dropbear[8510]: Child connection from 192.168.0.147:56580
Sat May  6 14:11:37 2017 kern.warn kernel: [81578.960000] ------------[ cut here ]------------
Sat May  6 14:11:37 2017 kern.warn kernel: [81578.970000] WARNING: CPU: 2 PID: 0 at net/core/skbuff.c:4196 skb_try_coalesce+0x228/0x35c()
Sat May  6 14:11:37 2017 kern.warn kernel: [81578.990000] Modules linked in: pppoe ppp_async pppox ppp_generic nf_conntrack_ipv6 iptable_nat ipt_REJECT ipt_MASQUERADE xt_time xt_tcpudp xt_tcpmss xt_statistic xt_state xt_recent xt_nat xt_multiport xt_mark xt_mac xt_limit xt_length xt_hl xt_helper xt_ecn xt_dscp xt_conntrack xt_connmark xt_connlimit xt_connbytes xt_comment xt_TEE xt_TCPMSS xt_REDIRECT xt_LOG xt_HL xt_DSCP xt_CLASSIFY slhc nf_reject_ipv4 nf_nat_redirect nf_nat_masquerade_ipv4 nf_conntrack_ipvSat May  6 14:11:37 2017 kern.warn kernel: [81579.220000] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.4.61 #0
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.230000] Stack : 00000000 00000000 804c6862 00000033 00000000 00000000 80470000 804e0000
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.230000] 	  87c4b9ec 80465c83 803e352c 00000002 00000000 804c367c 87c1dd3f 804fade0
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.230000] 	  00000000 80063258 80470000 804e0000 8046a188 8046a18c 803e8160 87c1dbec
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.230000] 	  00000003 80061014 87c1dd3f 804fade0 00000000 00000125 00000000 00c1dbec
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.230000] 	  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.230000] 	  ...
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.300000] Call Trace:
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.310000] [] show_stack+0x6c/0x88
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.320000] [] dump_stack+0x8c/0xc0
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.330000] [] warn_slowpath_common+0xa0/0xd0
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.340000] [] warn_slowpath_null+0x18/0x24
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.350000] [] skb_try_coalesce+0x228/0x35c
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.360000] [] tcp_try_coalesce+0x70/0xd4
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.370000] 
Sat May  6 14:11:37 2017 kern.warn kernel: [81579.370000] ---[ end trace 2800734bc845e5bf ]---

If necessary I can provide more information.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=764#comment2575