lockdep 实现

struct held_lock {
	/*
	 * One-way hash of the dependency chain up to this point. We
	 * hash the hashes step by step as the dependency chain grows.
	 *
	 * We use it for dependency-caching and we skip detection
	 * passes and dependency-updates if there is a cache-hit, so
	 * it is absolutely critical for 100% coverage of the validator
	 * to have a unique key value for every unique dependency path
	 * that can occur in the system, to make a unique hash value
	 * as likely as possible - hence the 64-bit width.
	 *
	 * The task struct holds the current hash value (initialized
	 * with zero), here we store the previous hash value:
	 */
	u64				prev_chain_key;
	unsigned long			acquire_ip;
	struct lockdep_map		*instance;
	struct lockdep_map		*nest_lock;
#ifdef CONFIG_LOCK_STAT
	u64 				waittime_stamp;
	u64				holdtime_stamp;
#endif
	/*
	 * class_idx is zero-indexed; it points to the element in
	 * lock_classes this held lock instance belongs to. class_idx is in
	 * the range from 0 to (MAX_LOCKDEP_KEYS-1) inclusive.
	 */
	unsigned int			class_idx:MAX_LOCKDEP_KEYS_BITS;
	/*
	 * The lock-stack is unified in that the lock chains of interrupt
	 * contexts nest ontop of process context chains, but we 'separate'
	 * the hashes by starting with 0 if we cross into an interrupt
	 * context, and we also keep do not add cross-context lock
	 * dependencies - the lock usage graph walking covers that area
	 * anyway, and we'd just unnecessarily increase the number of
	 * dependencies otherwise. [Note: hardirq and softirq contexts
	 * are separated from each other too.]
	 *
	 * The following field is used to detect when we cross into an
	 * interrupt context:
	 */
	unsigned int irq_context:2; /* bit 0 - soft, bit 1 - hard */
	unsigned int trylock:1;						/* 16 bits */

	unsigned int read:2;        /* see lock_acquire() comment */
	unsigned int check:1;       /* see lock_acquire() comment */
	unsigned int hardirqs_off:1;
	unsigned int references:12;					/* 32 bits */
	unsigned int pin_count;
};

源码

kernel/locking/lockdep.c 上的注释:

this code maps all the lock dependencies as they occur in a live kernel and will warn about the following classes of locking bugs:

• lock inversion scenarios
• circular lock dependencies
• hardirq/softirq safe/unsafe locking bugs

linux kernel 死锁问题分析（一） - 无人知晓的文章 - 知乎 https://zhuanlan.zhihu.com/p/22437191650

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