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Spinlocks can cause priority inversion in Rust no_std code

matklad.github.io 11 min read Editor score 7/10

The post examines spinlocks, priority inversion and CPU interrupts in the context of adding `no_std` support to synchronization libraries. The discussion highlights why swapping a blocking mutex for a spinlock can change system behavior.

What: Spinlocks are mutexes that keep a thread on-CPU, repeatedly attempting an atomic compare-and-swap until it acquires the lock.
How: Unlike OS mutexes, spinlocks do not block through a system call; blocking mutexes park threads in kernel queues and unpark them on release.
Why it matters: Replacing standard synchronization with a spinlock for no_std can waste CPU while waiting, making the swap an anti-pattern for systems code.

A blocking mutex parks a waiting thread in a kernel queue until it is unparked. Sketched from the article's own text.

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