Dealing with printk()
It's odd that printk() would pose so many problems for kernel development, given that it's essentially just a replacement for printf() that doesn't require linking the standard C library into the kernel.
And yet, it's famously a mess, full of edge cases, corner cases, deadlocks, race conditions and a variety of other tough-to-solve problems. The reason for this is, unlike printf(), the printk() system call has to produce reasonable behavior even when the entire system is in the midst of crashing. That's really the whole point—printk() needs to report errors and warnings that can be used to debug whatever strange and unexpected catastrophe has just hit a running system.
Trying to fix all the deadlocks and other problems at the same time would be too large a task for anyone, especially since each one is a special case defined by the particular context in which the printk() call appeared. But, sometimes a bunch of instances in a particular region of code can be addressed all together.
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