Kernel Deadlock Prevention (lockdep & Lock Ordering)

When to use

• Reviewing kernel code that acquires more than one lock, or a lock in a context where IRQs can fire.
• A lockdep splat ("possible circular locking dependency detected", "inconsistent lock state") needs a real fix, not a suppression.
• Designing lock ordering for a new subsystem: choosing a global order, using _nested() subclassing, and annotating with lockdep_assert_held*/lockdep_*pin_lock.
• Deciding whether a function may sleep given its lock context (spinlock held, IRQ disabled, RCU read-side, preempt disabled).

When not to use