Comment 0 for bug 1895550

I have a Raspberry Pi 4 Model B. I downloaded and flashed the image `ubuntu-18.04.5-preinstalled-server-arm64+raspi4.img` (md5 = b75105bf4e27cbcc44dc471becc8907d), which is the currently recommended release for this hardware on the Ubuntu.com website.

Booting reaches this point where it tries to do something with the SD card, then fails:

[ 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

Afterwards, about once per minute, it outputs an error message like this:

[ 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

The only modifications I made to the filesystem were to the `user-data` and `network-config` files for headless setup. I do not believe these modifications are relevant.

I downloaded and flashed the previous release, `ubuntu-18.04.4-preinstalled-server-arm64+raspi4.img`, and that release booted successfully.