我将 Raspberry Pi 4 的 Ubuntu 18.04.5 映像 ( ubuntu-18.04.5-preinstalled-server-arm64+raspi4.img) 刷入 SD 卡，并通过 5V GPIO 引脚为 RPi4 供电。
启动时，会出现这种情况：
[ 4.352613] random: fast init done
[ 4.414200] mmc0: new ultra high speed DDR50 SDHC card at address aaaa
[ 4.423077] mmcblk0: mmc0:aaaa SC32G 29.7 GiB
[ 4.431244] mmc1: new high speed SDIO card at address 0001
[ 4.437267] mmcblk0: p1 p2
然后在打印之前有 24 秒的暂停：
[ 28.006460] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[ 28.012484] rcu: 1-...0: (7 ticks this GP) idle=1d6/1/0x4000000000000000 softirq=80/81 fqs=7
[ 28.021231] (detected by 3, t=5893 jiffies, g=-379, q=2)
[ 28.026710] Task dump for CPU 1:
[ 28.029984] swapper/0 R running task 0 1 0 0x0000002a
[ 28.037143] Call trace:
[ 28.039636] __switch_to+0xcc/0x208
[ 28.043179] console_unlock+0x4f8/0x600
[ 28.047076] rcu: rcu_sched kthread starved for 1001 jiffies! g-379 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=3
[ 28.057405] rcu: RCU grace-period kthread stack dump:
[ 28.062529] rcu_sched I 0 10 2 0x00000028
[ 28.068098] Call trace:
[ 28.070580] __switch_to+0xcc/0x208
[ 28.074123] __schedule+0x2c4/0x7b0
[ 28.077663] schedule+0x38/0xa8
[ 28.080851] schedule_timeout+0x1a0/0x378
[ 28.084920] rcu_gp_kthread+0x688/0xa10
[ 28.088813] kthread+0x124/0x128
[ 28.092089] ret_from_fork+0x10/0x1c
大约一分钟后，它会打印出类似的痕迹：
[ 92.006458] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[ 92.012475] rcu: 1-...0: (7 ticks this GP) idle=1d6/1/0x4000000000000000 softirq=80/81 fqs=23
[ 92.021308] (detected by 3, t=21893 jiffies, g=-379, q=2)
[ 92.026874] Task dump for CPU 1:
[ 92.030147] swapper/0 R running task 0 1 0 0x0000002a
[ 92.037304] Call trace:
[ 92.039788] __switch_to+0xcc/0x208
[ 92.043328] console_unlock+0x4f8/0x600
[ 92.047223] rcu: rcu_sched kthread starved for 1001 jiffies! g-379 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=3
[ 92.057552] rcu: RCU grace-period kthread stack dump:
[ 92.062675] rcu_sched I 0 10 2 0x00000028
[ 92.068242] Call trace:
[ 92.070726] __switch_to+0xcc/0x208
[ 92.074265] __schedule+0x2c4/0x7b0
[ 92.077804] schedule+0x38/0xa8
[ 92.080991] schedule_timeout+0x1a0/0x378
[ 92.085060] rcu_gp_kthread+0x688/0xa10
[ 92.088952] kthread+0x124/0x128
[ 92.092227] ret_from_fork+0x10/0x1c
等等，几乎每一分钟都是如此。
我没有收到控制台登录提示，并且也没有我期望的与启动相关的消息。
我该如何进一步诊断这个问题？
答案1
Raspberry Pi 4（64 位）的 18.04.5 版本目前似乎有问题。我提交了Ubuntu 项目的一个问题以供进一步讨论。安装 18.04.4 映像有效。