Same. I usually end up adding a ton of pr_warn statements to kernel code and progressively dig deeper and deeper as I figure out which path every function ends

Same. I usually end up adding a ton of pr_warn statements to kernel code and progressively dig deeper and deeper as I figure out which path every function ends up taking, with a kernel recompile + re-flashing + rebooting in between every step. I sorely wish the kernel had better instrumentation for figuring out where error returns originate from. There are debug prints in some places which can be enabled (if you're lucky, your kernel is even compiled to let you enable those at runtime, without recompiling!), however most of the kernel clearly does not have a culture of debug logging whenever it returns an error.