Goal

Protection of a shared resource (often a data structure) from concurrent access

Primitive & Alternative

// Global,statically defined/initialized at compile time
static DEFINE_SPINLOCK(xxx_lock);

// Usage
unsigned long flags;

spin_lock_isrqsave(&xxx_lock, flags);
/* critical section */
spin_unlock_irqrestore(&xxx_lock, flags);

spinlock_t xxx_lock;

// __init, dynamically initialized at runtime
spin_lock_init(&xxx_lock);

// Usage
unsigned long flags;

spin_lock_irqsave(&xxx_lock, flags);
/* critical section */
spin_unlock_irqrestore(&xxx_lock, flags);

Reader-Writer

For a shared resource in which the resource is mostly read from, a read-writer lock can be useful since multiple readers can be in the same critical region at the same time.

rwlock_t xxx_lock = __RW_LOCK_UNLOCKED(xxx_lock);

// Usage
unsigned long flags;

read_lock_irqsave(&xxx_lock, flags);
/* critical section that only reads the info */
read_unlock_irqrestore(&xxx_lock, flags);

write_lock_irqsave(&xxx_lock, flags);
/* read and write exclusive access to the info */
write_unlock_irqrestore(&xxx_lock, flags);

Useful for complex data structures like linked lists, where you need to search for an entry without changing the lock itself

Non-Interrupt Handler Spinlocks

IFF you know that the spinlocks are never used in interrupt handlers, you can use the non-irq versions

spin_lock(&lock)
/* critical section */
spin_unlock(&lock)