How to printk synchronously

[aleave]

Hi everyone,

I'm modifying kernel code and running into system dead-lock issues. I have printk statements to try to retrieve info about the freeze after I do a hard shutdown, but printk is asynchronous so /var/log/kern.log only shows NULL character gibberish instead (^@^@^@^@). Is there a way to make printk synchronous? I have looked at people using [printk_sync](https://lore.kernel.org/patchwork/patch/671535/) and [printk.synchronous](https://stackoverflow.com/questions/26413750/how-to-avoid-printk-log-dropping-in-linux-kernel) variables as recently as 2017, but I don't see any reference to these anymore in the kernel version I have (5.4).

Thanks for the help.
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