IF i hit the WAN interface with high load i will randomly crash the driver for ethernet with:
[ 844.322880] ------------[ cut here ]------------
[ 844.327546] WARNING: CPU: 0 PID: 0 at net/sched/sch_generic.c:448 0x80465954
[ 844.334586] NETDEV WATCHDOG: eth0 (mtk_soc_eth): transmit queue 0 timed out
[ 844.341564] Modules linked in: iptable_nat xt_state xt_nat xt_conntrack xt_REDIRECT xt_MASQUERADE xt_FLOWOFFLOAD wireguard nf_nat nf_flow_table_hw nf_flow_table nf_conntrack_rtcache nf_conntrack_netlink nf_conntrack mt7915e mt76 mac80211 libchacha20poly1305 libblake2s ipt_REJECT cfg8t
[ 844.341748] ip_set_hash_ipmark ip_set_hash_ip ip_set_bitmap_port ip_set_bitmap_ipmac ip_set_bitmap_ip ip_set nfnetlink nf_log_ipv6 nf_log_common ip6table_mangle ip6table_filter ip6_tables ip6t_REJECT x_tables nf_reject_ipv6 swconfig ip6_udp_tunnel udp_tunnel ipcomp6 xfrm6_tunnel espn
[ 844.485027] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G C 5.4.111 #0
[ 844.492414] Stack : 00000000 80830000 00000122 8007fe50 00000000 00000000 00000000 00000000
[ 844.500751] 00000000 00000000 00000000 00000000 00000000 00000001 8fc1fd28 92673a1f
[ 844.509069] 8fc1fdc0 00000000 00000000 00000000 00000038 805b8ac4 342e3520 3131312e
[ 844.517386] 00000000 00000029 00000000 000766a3 00000000 8fc1fd08 00000000 000001c0
[ 844.525703] 00000009 00000000 806ae56c 80670000 00000003 80357e10 00000000 80800000
[ 844.534021] ...
[ 844.536451] Call Trace:
[ 844.536465] [<8007fe50>] 0x8007fe50
[ 844.542360] [<805b8ac4>] 0x805b8ac4
[ 844.545830] [<80357e10>] 0x80357e10
[ 844.549299] [<8000ba08>] 0x8000ba08
[ 844.552768] [<8000ba10>] 0x8000ba10
[ 844.556237] [<806b0000>] 0x806b0000
[ 844.559705] [<8059f08c>] 0x8059f08c
[ 844.563174] [<80080018>] 0x80080018
[ 844.566641] [<80465954>] 0x80465954
[ 844.570109] [<8002c098>] 0x8002c098
[ 844.573579] [<80465954>] 0x80465954
[ 844.577048] [<80465954>] 0x80465954
[ 844.580516] [<8002c184>] 0x8002c184
[ 844.583986] [<80465954>] 0x80465954
[ 844.587455] [<8009b1dc>] 0x8009b1dc
[ 844.590924] [<803e87a8>] 0x803e87a8
[ 844.594391] [<804655d4>] 0x804655d4
[ 844.597860] [<80096f88>] 0x80096f88
[ 844.601330] [<800aac2c>] 0x800aac2c
[ 844.604799] [<80097444>] 0x80097444
[ 844.608269] [<800865fc>] 0x800865fc
[ 844.611739] [<805bf2b8>] 0x805bf2b8
[ 844.615208] [<80301c80>] 0x80301c80
[ 844.618674] [<80301b24>] 0x80301b24
[ 844.622146] [<8003143c>] 0x8003143c
[ 844.625615] [<803015d8>] 0x803015d8
[ 844.629085] [<80007128>] 0x80007128
[ 844.632551]
[ 844.634293] ---[ end trace 2962b589f1840a4c ]---
[ 844.638990] mtk_soc_eth 1e100000.ethernet eth0: transmit timed out
[ 844.645683] mtk_soc_eth 1e100000.ethernet eth0: Link is Down
[ 844.679706] mtk_soc_eth 1e100000.ethernet eth0: configuring for fixed/rgmii link mode
[ 844.687653] mtk_soc_eth 1e100000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
The link goes AWOL then for some time, but eventually recovers. It causes really bad connection issues for MT7621 hardware.
A good way to trigger it is to run an iperf3 test through the router over wifi (iperf3 client on wifi, iperf3 server downstream of the routers wan interface.)