I use openwrt 19.07.x (kernel 4.19.108) with R64, sometimes kernel stall on usbnet_change_mtu [usbnet] at kernel booting time. Any ideas? Thanks.
[ 93.989154] rcu: INFO: rcu_sched self-detected stall on CPU
[ 93.994915] rcu: 0-....: (5999 ticks this GP) idle=2fa/1/0x4000000000000004 softirq=3692/3693 fqs=2989
[ 94.004687] rcu: (t=6001 jiffies g=1425 q=43764)
[ 94.009623] Task dump for CPU 0:
[ 94.012945] kworker/0:2 R running task 0 633 2 0x0000002a
[ 94.020259] Workqueue: events usbnet_change_mtu [usbnet]
[ 94.025732] Call trace:
[ 94.028253] dump_backtrace+0x0/0x128
[ 94.032024] show_stack+0x14/0x20
[ 94.035438] sched_show_task+0x10c/0x138
[ 94.039478] dump_cpu_task+0x40/0x4c
[ 94.043162] rcu_dump_cpu_stacks+0xa8/0xfc
[ 94.047380] rcu_check_callbacks+0x328/0x6f8
[ 94.051780] update_process_times+0x2c/0x58
[ 94.056090] tick_sched_handle.isra.5+0x3c/0x48
[ 94.060757] tick_sched_timer+0x48/0x88
[ 94.064707] __hrtimer_run_queues+0xb4/0x1a8
[ 94.069104] hrtimer_interrupt+0x110/0x278
[ 94.073326] arch_timer_handler_phys+0x2c/0x40
[ 94.077905] handle_percpu_devid_irq+0x80/0x150
[ 94.082571] generic_handle_irq+0x24/0x38
[ 94.086700] __handle_domain_irq+0x88/0xb0
[ 94.090917] gic_handle_irq+0x60/0xa0
[ 94.094687] el1_irq+0xb0/0x140
[ 94.097932] usbnet_disconnect+0x300/0x838 [usbnet]
[ 94.102960] usbnet_disconnect+0x380/0x838 [usbnet]
[ 94.107988] usbnet_disconnect+0x7bc/0x838 [usbnet]
[ 94.113015] tasklet_action_common.isra.3+0x94/0x100
[ 94.118129] tasklet_action+0x24/0x30
[ 94.121898] __do_softirq+0xe4/0x1e8
[ 94.125579] irq_exit+0x70/0xd0
[ 94.128811] __handle_domain_irq+0x8c/0xb0
[ 94.133029] gic_handle_irq+0x60/0xa0
[ 94.136799] el1_irq+0xb0/0x140
[ 94.140034] xhci_urb_dequeue+0x3d4/0x430
[ 94.144166] unlink1+0x124/0x140
[ 94.147489] usb_hcd_unlink_urb+0xb0/0xe0
[ 94.151618] usb_unlink_urb+0x24/0x48
[ 94.155392] usbnet_status_stop+0xc0/0x158 [usbnet]
[ 94.160420] usbnet_change_mtu+0xc8/0x4f0 [usbnet]
[ 94.165358] usbnet_change_mtu+0x4a0/0x4f0 [usbnet]
[ 94.170385] process_one_work+0x200/0x350
[ 94.174513] worker_thread+0x260/0x468
[ 94.178375] kthread+0x118/0x128
[ 94.181697] ret_from_fork+0x10/0x1c
[ 100.329165] rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-... } 6498 jiffies s: 9 root: 0x1/.
[ 100.339771] rcu: blocking rcu_node structures:
[ 100.344349] Task dump for CPU 0:
[ 100.347671] kworker/0:2 R running task 0 633 2 0x0000002a
[ 100.354996] Workqueue: events usbnet_change_mtu [usbnet]
[ 100.360477] Call trace:
[ 100.362998] __switch_to+0xfc/0x108
[ 100.366592] process_one_work+0x200/0x350
[ 100.370726] worker_thread+0x260/0x468
[ 100.374589] kthread+0x118/0x128
[ 100.377912] ret_from_fork+0x10/0x1c
[ 274.019168] rcu: INFO: rcu_sched self-detected stall on CPU
[ 274.024928] rcu: 0-....: (23984 ticks this GP) idle=2fa/1/0x4000000000000004 softirq=3692/3693 fqs=11981
[ 274.034880] rcu: (t=24004 jiffies g=1425 q=45746)
[ 274.039908] Task dump for CPU 0:
[ 274.043230] kworker/0:2 R running task 0 633 2 0x0000002a
[ 274.050539] Workqueue: events usbnet_change_mtu [usbnet]
[ 274.056011] Call trace:
[ 274.058532] dump_backtrace+0x0/0x128
[ 274.062303] show_stack+0x14/0x20
[ 274.065718] sched_show_task+0x10c/0x138
[ 274.069758] dump_cpu_task+0x40/0x4c
[ 274.073441] rcu_dump_cpu_stacks+0xa8/0xfc
[ 274.077659] rcu_check_callbacks+0x328/0x6f8
[ 274.082058] update_process_times+0x2c/0x58
[ 274.086370] tick_sched_handle.isra.5+0x3c/0x48
[ 274.091037] tick_sched_timer+0x48/0x88
[ 274.094986] __hrtimer_run_queues+0xb4/0x1a8
[ 274.099384] hrtimer_interrupt+0x110/0x278
[ 274.103604] arch_timer_handler_phys+0x2c/0x40
[ 274.108184] handle_percpu_devid_irq+0x80/0x150
[ 274.112851] generic_handle_irq+0x24/0x38
[ 274.116980] __handle_domain_irq+0x88/0xb0
[ 274.121197] gic_handle_irq+0x60/0xa0
[ 274.124968] el1_irq+0xb0/0x140
[ 274.128201] __do_softirq+0x9c/0x1e8
[ 274.131883] irq_exit+0x70/0xd0
[ 274.135115] __handle_domain_irq+0x8c/0xb0
[ 274.139333] gic_handle_irq+0x60/0xa0
[ 274.143103] el1_irq+0xb0/0x140
[ 274.146339] xhci_urb_dequeue+0x3d4/0x430
[ 274.150471] unlink1+0x124/0x140
[ 274.153793] usb_hcd_unlink_urb+0xb0/0xe0
[ 274.157922] usb_unlink_urb+0x24/0x48
[ 274.161708] usbnet_status_stop+0xc0/0x158 [usbnet]
[ 274.166736] usbnet_change_mtu+0xc8/0x4f0 [usbnet]
[ 274.171675] usbnet_change_mtu+0x4a0/0x4f0 [usbnet]
[ 274.176702] process_one_work+0x200/0x350
[ 274.180830] worker_thread+0x260/0x468
[ 274.184692] kthread+0x118/0x128
[ 274.188014] ret_from_fork+0x10/0x1c
[ 284.649167] rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-... } 24930 jiffies s: 9 root: 0x1/.
[ 284.659860] rcu: blocking rcu_node structures:
[ 284.664437] Task dump for CPU 0:
[ 284.667758] kworker/0:2 R running task 0 633 2 0x0000002a
[ 284.675083] Workqueue: events usbnet_change_mtu [usbnet]
[ 284.680564] Call trace:
[ 284.683084] __switch_to+0xfc/0x108
[ 284.686677] process_one_work+0x200/0x350
[ 284.690815] worker_thread+0x260/0x468
[ 284.694678] kthread+0x118/0x128
[ 284.698000] ret_from_fork+0x10/0x1c