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> However, printk can block (while allocating memory)

No, printk() is magic. It can be called even in NMI context, which is a worse place. Quoting https://lwn.net/Articles/800946/, "[...] kernel code must be able to call printk() from any context. Calls from atomic context prevent it from blocking; calls from non-maskable interrupts (NMIs) can even rule out the use of spinlocks. [...]"

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This is really good to know. I had assumed it could block when allocating memory for the formatted string buffer, but the rationale explained in that article makes a lot of sense. Being able to use printk simplifes things a lot.

Also: allocating memory with GFP_ATOMIC doesn't sleep.

now that is technical leadership.

If you have to rely on printf debugging, you go to epic lengths to ensure printf always works.

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