Mastering Linux Kernel Development

Reader-writer semaphores

This interface is an implementation of sleeping reader-writer exclusion, which serves as an alternative for spinning ones. Reader-writer semaphores are represented by struct rw_semaphore, declared in the kernel header <linux/rwsem.h>:

struct rw_semaphore {
        atomic_long_t count;
        struct list_head wait_list;
        raw_spinlock_t wait_lock;
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
       struct optimistic_spin_queue osq; /* spinner MCS lock */
       /*
       * Write owner. Used as a speculative check to see
       * if the owner is running on the cpu.
       */
      struct task_struct *owner;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
     struct lockdep_map dep_map;
#endif
};

This structure is identical to that of a mutex, and is designed to support optimistic spinning with ...