最近在移植一个rk3562的板子，发现内核启动会卡住，无输入输出。
在正常的rootfs中，在串口手动触发panic后，也无输入输出。
# echo c > /proc/sysrq-trigger
仔细查看内核日志，有一个：
[ 0.409106] ramoops: dmesg-0 0x18000@0x0000000000110000
[ 0.414754] ramoops: dmesg-1 0x18000@0x0000000000128000
[ 0.420809] ramoops: console 0x80000@0x0000000000140000
[ 0.426426] ramoops: pmsg 0x30000@0x00000000001c0000
[ 0.431769] printk: console [ramoops-1] enabled
怀疑是panic被打印到其它地方去了。搜内核，发现了：Documentation/admin-guide/ramoops.rst
尝试关掉pstore，仍然不解决问题。
drivers/tty/sysrq.c 加调试：
static void sysrq_handle_crash(int key)
{
/* release the RCU read lock before crashing */
rcu_read_unlock();
printk("---------------- sysrq triggerred crash\n");
panic("sysrq triggered crash\n");
}
printk都没打出来，注释掉panic后，可以打出来。怀疑是panic()的问题。
查看内核启动日志，有：
[ 0.756071] printk: console [ttyFIQ0]: printing thread started
然后搜到了一篇文章。内核为printk启动了一个线程。
然后panic函数里面有：
pr_flush是等待print thread完成，再后面加一个 while(1); 结果panic日志打出来。然后怀疑是时间太短了。改成30s。就ok了。
[ 1.145480] Run /sbin/init as init process
[ 1.145483] with arguments:
[ 1.145487] /sbin/init
[ 1.145489] #t-10/08/2024
[ 1.145492] with environment:
[ 1.145495] HOME=/
[ 1.145497] TERM=linux
[ 1.145499] storagemedia=emmc
[ 1.150147] run /sbin/init return -2
[ 1.150157] Run /etc/init as init process
[ 1.150160] with arguments:
[ 1.150164] /etc/init
[ 1.150167] #t-10/08/2024
[ 1.150169] with environment:
[ 1.150172] HOME=/
[ 1.150174] TERM=linux
[ 1.150176] storagemedia=emmc
[ 1.150394] run /etc/init return -2
[ 1.150398] Run /bin/init as init process
[ 1.150400] with arguments:
[ 1.150403] /bin/init
[ 1.150405] #t-10/08/2024
[ 1.150407] with environment:
[ 1.150410] HOME=/
[ 1.150412] TERM=linux
[ 1.150414] storagemedia=emmc
[ 1.150461] run /bin/init return -2
[ 1.150464] Run /bin/sh as init process
[ 1.150466] with arguments:
[ 1.150468] /bin/sh
[ 1.150471] #t-10/08/2024
[ 1.150473] with environment:
[ 1.150475] HOME=/
[ 1.150477] TERM=linux
[ 1.150480] storagemedia=emmc
[ 1.150551] run /bin/sh return -2
[ 1.150555] Kernel panic - not syncing:
[ 1.150557] No working init found. Try passing init= option to kernel. See Linux Documentation/admin-guide/init.rst for guidance.
[ 1.150560] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.209-rt89-g17a4e1a-dirty #12
[ 1.150566] Hardware name: TL3562-MiniEVM (DT)
[ 1.150570] Call trace:
[ 1.150571] dump_backtrace+0x0/0x1f0
[ 1.150585] show_stack+0x1c/0x24
[ 1.150591] dump_stack_lvl+0xe0/0x104
[ 1.150599] dump_stack+0x14/0x30
[ 1.150605] panic+0xf8/0x374
[ 1.150611] kernel_init+0x1d4/0x1ec
[ 1.150618] ret_from_fork+0x10/0x20
[ 1.399234] dw-mipi-dsi-rockchip ffb10000.dsi: [drm:dw_mipi_dsi_bridge_atomic_enable] final DSI-Link bandwidth: 996 x 4 Mbps
参考：
printk: introduce printing kernel thread
https://lwn.net/Articles/716319/