Linux Device Drivers | Concurrency and Race Conditions

<asm/semaphore.h> (not found)

The include file that defines semaphores and the operations on them.

DECLARE_MUTEX(name);
DECLARE_MUTEX_LOCKED(name);

Two macros for declaring and initializing a semaphore used in mutual exclusion mode.

void init_MUTEX(struct semaphore *sem);
void init_MUTEX_LOCKED(struct semaphore *sem);

These two functions can be used to initialize a semaphore at runtime.

void down(struct semaphore *sem);
int down_interruptible(struct semaphore *sem);
int down_trylock(struct semaphore *sem);
void up(struct semaphore *sem);

Lock and unlock a semaphore. down puts the calling process into an uninterruptible sleep if need be; down_interruptible, instead, can be interrupted by a signal. down_trylock does not sleep; instead, it returns immediately if the semaphore is unavailable. Code that locks a semaphore must eventually unlock it with up.

struct rw_semaphore;
init_rwsem(struct rw_semaphore *sem);

The reader/writer version of semaphores and the function that initializes it.

void down_read(struct rw_semaphore *sem);
int down_read_trylock(struct rw_semaphore *sem);
void up_read(struct rw_semaphore *sem);

Functions for obtaining and releasing read access to a reader/writer semaphore.

void down_write(struct rw_semaphore *sem)
int down_write_trylock(struct rw_semaphore *sem)
void up_write(struct rw_semaphore *sem)
void downgrade_write(struct rw_semaphore *sem)

Functions for managing write access to a reader/writer semaphore.

<linux/completion.h>

DECLARE_COMPLETION(name);
init_completion(struct completion *c);
INIT_COMPLETION(struct completion c);

The include file describing the Linux completion mechanism, and the normal methods for initializing completions. INIT_COMPLETION should be used only to reinitialize a completion that has been previously used.

void wait_for_completion(struct completion *c);

Wait for a completion event to be signaled.

void complete(struct completion *c);
void complete_all(struct completion *c);

Signal a completion event. complete wakes, at most, one waiting thread, while complete_all wakes all waiters.

void complete_and_exit(struct completion *c, long retval);

Signals a completion event by calling complete and calls exit for the current thread.

<linux/spinlock.h>

spinlock_t lock = SPIN_LOCK_UNLOCKED;
spin_lock_init(spinlock_t *lock);

The include file defining the spinlock interface and the two ways of initializing locks.

void spin_lock(spinlock_t *lock);
void spin_lock_irqsave(spinlock_t *lock, unsigned long flags);
void spin_lock_irq(spinlock_t *lock);
void spin_lock_bh(spinlock_t *lock);

The various ways of locking a spinlock and, possibly, disabling interrupts.

int spin_trylock(spinlock_t *lock);
int spin_trylock_bh(spinlock_t *lock);

Non-spinning versions of the above functions; these return 0 in case of failure to obtain the lock, nonzero otherwise.

void spin_unlock(spinlock_t *lock);
void spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags);
void spin_unlock_irq(spinlock_t *lock);
void spin_unlock_bh(spinlock_t *lock);

The corresponding ways of releasing a spinlock.

rwlock_t lock = RW_LOCK_UNLOCKED;
rwlock_init(rwlock_t *lock);

The two ways of initializing reader/writer locks.

void read_lock(rwlock_t *lock);
void read_lock_irqsave(rwlock_t *lock, unsigned long flags);
void read_lock_irq(rwlock_t *lock);
void read_lock_bh(rwlock_t *lock);

Functions for obtaining read access to a reader/writer lock.

void read_unlock(rwlock_t *lock);
void read_unlock_irqrestore(rwlock_t *lock, unsigned long flags);
void read_unlock_irq(rwlock_t *lock);
void read_unlock_bh(rwlock_t *lock);

Functions for releasing read access to a reader/writer spinlock.

void write_lock(rwlock_t *lock);
void write_lock_irqsave(rwlock_t *lock, unsigned long flags);
void write_lock_irq(rwlock_t *lock);
void write_lock_bh(rwlock_t *lock);

Functions for obtaining write access to a reader/writer lock.

void write_unlock(rwlock_t *lock);
void write_unlock_irqrestore(rwlock_t *lock, unsigned long flags);
void write_unlock_irq(rwlock_t *lock);
void write_unlock_bh(rwlock_t *lock);

Functions for releasing write access to a reader/writer spinlock.

<linux/rwsem.h>

struct rw_semaphore;
init_rwsem(struct rw_semaphore *sem);

The reader/writer version of semaphores and the function that initializes it.

void down_read(struct rw_semaphore *sem);
int down_read_trylock(struct rw_semaphore *sem);
void up_read(struct rw_semaphore *sem);

Functions for obtaining and releasing read access to a reader/writer semaphore.

void down_write(struct rw_semaphore *sem)
int down_write_trylock(struct rw_semaphore *sem)
void up_write(struct rw_semaphore *sem)
void downgrade_write(struct rw_semaphore *sem)

Functions for managing write access to a reader/writer semaphore.