printk() - The Most Useful Tool is Now Showing its Age
summary
printk is the kernel printf that still uses a single fixed-size ring buffer with log levels 1–8 and metadata, and its 1998 spinlock introduced in 1998 plus the later console_lock serializes output and can live-lock one CPU make high‑CPU systems stall when many CPUs emit logs; the codebase evolves (2012 message layout, exclusive_console in 2011) and fixes include per-CPU buffers + irq_work to flush promptly and an NMI-safe path and printk_safe multiplexer that reduce but do not fully eliminate lost or blocking output on panic.
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