Thanks. However, as you know now I even couldn't get into the failsave mode. So it is impossible for me to set the parameter at the console. What I do is to change the
ignore_loglevel = true directly in the source code
/build_dir/target-mips_34kc_musl/linux-ar71xx_myimg/linux-4.14.254/kernel/printk/printk.c.
So far seems that the console print is still as before. Any thought? Thanks