/* rwsem-spinlock.c: R/W semaphores: contention handling functions for * generic spinlock implementation * * Copyright (c) 2001 David Howells (dhowells@redhat.com). * - Derived partially from idea by Andrea Arcangeli <andrea@suse.de> * - Derived also from comments by Linus */#include <linux/rwsem.h>#include <linux/sched.h>#include <linux/export.h> enum rwsem_waiter_type { RWSEM_WAITING_FOR_WRITE, RWSEM_WAITING_FOR_READ}; struct rwsem_waiter { struct list_head list; struct task_struct *task; enum rwsem_waiter_type type;}; int rwsem_is_locked(struct rw_semaphore *sem){ int ret = 1; unsigned long flags; if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) { ret = (sem->activity != 0); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); } return ret;}EXPORT_SYMBOL(rwsem_is_locked); /* * initialise the semaphore */void __init_rwsem(struct rw_semaphore *sem, const char *name, struct lock_class_key *key){#ifdef CONFIG_DEBUG_LOCK_ALLOC /* * Make sure we are not reinitializing a held semaphore: */ debug_check_no_locks_freed((void *)sem, sizeof(*sem)); lockdep_init_map(&sem->dep_map, name, key, 0);#endif sem->activity = 0; raw_spin_lock_init(&sem->wait_lock); INIT_LIST_HEAD(&sem->wait_list);}EXPORT_SYMBOL(__init_rwsem); /* * handle the lock release when processes blocked on it that can now run * - if we come here, then: * - the 'active count' _reached_ zero * - the 'waiting count' is non-zero * - the spinlock must be held by the caller * - woken process blocks are discarded from the list after having task zeroed * - writers are only woken if wakewrite is non-zero */static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite){ struct rwsem_waiter *waiter; struct task_struct *tsk; int woken; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (waiter->type == RWSEM_WAITING_FOR_WRITE) { if (wakewrite) /* Wake up a writer. Note that we do not grant it the * lock - it will have to acquire it when it runs. */ wake_up_process(waiter->task); goto out; } /* grant an infinite number of read locks to the front of the queue */ woken = 0; do { struct list_head *next = waiter->list.next; list_del(&waiter->list); tsk = waiter->task; smp_mb(); waiter->task = NULL; wake_up_process(tsk); put_task_struct(tsk); woken++; if (next == &sem->wait_list) break; waiter = list_entry(next, struct rwsem_waiter, list); } while (waiter->type != RWSEM_WAITING_FOR_WRITE); sem->activity += woken; out: return sem;} /* * wake a single writer */static inline struct rw_semaphore *__rwsem_wake_one_writer(struct rw_semaphore *sem){ struct rwsem_waiter *waiter; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); wake_up_process(waiter->task); return sem;} /* * get a read lock on the semaphore */void __sched __down_read(struct rw_semaphore *sem){ struct rwsem_waiter waiter; struct task_struct *tsk; unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (sem->activity >= 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity++; raw_spin_unlock_irqrestore(&sem->wait_lock, flags); goto out; } tsk = current; set_task_state(tsk, TASK_UNINTERRUPTIBLE); /* set up my own style of waitqueue */ waiter.task = tsk; waiter.type = RWSEM_WAITING_FOR_READ; get_task_struct(tsk); list_add_tail(&waiter.list, &sem->wait_list); /* we don't need to touch the semaphore struct anymore */ raw_spin_unlock_irqrestore(&sem->wait_lock, flags); /* wait to be given the lock */ for (;;) { if (!waiter.task) break; schedule(); set_task_state(tsk, TASK_UNINTERRUPTIBLE); } tsk->state = TASK_RUNNING; out: ;} /* * trylock for reading -- returns 1 if successful, 0 if contention */int __down_read_trylock(struct rw_semaphore *sem){ unsigned long flags; int ret = 0; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (sem->activity >= 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity++; ret = 1; } raw_spin_unlock_irqrestore(&sem->wait_lock, flags); return ret;} /* * get a write lock on the semaphore */void __sched __down_write_nested(struct rw_semaphore *sem, int subclass){ struct rwsem_waiter waiter; struct task_struct *tsk; unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); /* set up my own style of waitqueue */ tsk = current; waiter.task = tsk; waiter.type = RWSEM_WAITING_FOR_WRITE; list_add_tail(&waiter.list, &sem->wait_list); /* wait for someone to release the lock */ for (;;) { /* * That is the key to support write lock stealing: allows the * task already on CPU to get the lock soon rather than put * itself into sleep and waiting for system woke it or someone * else in the head of the wait list up. */ if (sem->activity == 0) break; set_task_state(tsk, TASK_UNINTERRUPTIBLE); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); schedule(); raw_spin_lock_irqsave(&sem->wait_lock, flags); } /* got the lock */ sem->activity = -1; list_del(&waiter.list); raw_spin_unlock_irqrestore(&sem->wait_lock, flags);} void __sched __down_write(struct rw_semaphore *sem){ __down_write_nested(sem, 0);} /* * trylock for writing -- returns 1 if successful, 0 if contention */int __down_write_trylock(struct rw_semaphore *sem){ unsigned long flags; int ret = 0; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (sem->activity == 0) { /* got the lock */ sem->activity = -1; ret = 1; } raw_spin_unlock_irqrestore(&sem->wait_lock, flags); return ret;} /* * release a read lock on the semaphore */void __up_read(struct rw_semaphore *sem){ unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); if (--sem->activity == 0 && !list_empty(&sem->wait_list)) sem = __rwsem_wake_one_writer(sem); raw_spin_unlock_irqrestore(&sem->wait_lock, flags);} /* * release a write lock on the semaphore */void __up_write(struct rw_semaphore *sem){ unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); sem->activity = 0; if (!list_empty(&sem->wait_list)) sem = __rwsem_do_wake(sem, 1); raw_spin_unlock_irqrestore(&sem->wait_lock, flags);} /* * downgrade a write lock into a read lock * - just wake up any readers at the front of the queue */void __downgrade_write(struct rw_semaphore *sem){ unsigned long flags; raw_spin_lock_irqsave(&sem->wait_lock, flags); sem->activity = 1; if (!list_empty(&sem->wait_list)) sem = __rwsem_do_wake(sem, 0); raw_spin_unlock_irqrestore(&sem->wait_lock, flags);}
/* rwsem-spinlock.c: R/W semaphores: contention handling functions for
* generic spinlock implementation
*
* Copyright (c) 2001 David Howells (dhowells@redhat.com).
* - Derived partially from idea by Andrea Arcangeli <andrea@suse.de>
* - Derived also from comments by Linus
*/
#include <linux/rwsem.h>
#include <linux/sched.h>
#include <linux/export.h>
enum rwsem_waiter_type {
RWSEM_WAITING_FOR_WRITE,
RWSEM_WAITING_FOR_READ
};
struct rwsem_waiter {
struct list_head list;
struct task_struct *task;
enum rwsem_waiter_type type;
};
int rwsem_is_locked(struct rw_semaphore *sem)
{
int ret = 1;
unsigned long flags;
if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) {
ret = (sem->activity != 0);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
}
return ret;
}
EXPORT_SYMBOL(rwsem_is_locked);
/*
* initialise the semaphore
*/
void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/*
* Make sure we are not reinitializing a held semaphore:
*/
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map(&sem->dep_map, name, key, 0);
#endif
sem->activity = 0;
raw_spin_lock_init(&sem->wait_lock);
INIT_LIST_HEAD(&sem->wait_list);
}
EXPORT_SYMBOL(__init_rwsem);
/*
* handle the lock release when processes blocked on it that can now run
* - if we come here, then:
* - the 'active count' _reached_ zero
* - the 'waiting count' is non-zero
* - the spinlock must be held by the caller
* - woken process blocks are discarded from the list after having task zeroed
* - writers are only woken if wakewrite is non-zero
*/
static inline struct rw_semaphore *
__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
{
struct rwsem_waiter *waiter;
struct task_struct *tsk;
int woken;
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
if (wakewrite)
/* Wake up a writer. Note that we do not grant it the
* lock - it will have to acquire it when it runs. */
wake_up_process(waiter->task);
goto out;
}
/* grant an infinite number of read locks to the front of the queue */
woken = 0;
do {
struct list_head *next = waiter->list.next;
list_del(&waiter->list);
tsk = waiter->task;
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
woken++;
if (next == &sem->wait_list)
break;
waiter = list_entry(next, struct rwsem_waiter, list);
} while (waiter->type != RWSEM_WAITING_FOR_WRITE);
sem->activity += woken;
out:
return sem;
}
/*
* wake a single writer
*/
static inline struct rw_semaphore *
__rwsem_wake_one_writer(struct rw_semaphore *sem)
{
struct rwsem_waiter *waiter;
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
wake_up_process(waiter->task);
return sem;
}
/*
* get a read lock on the semaphore
*/
void __sched __down_read(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
struct task_struct *tsk;
unsigned long flags;
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity++;
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
goto out;
}
tsk = current;
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
/* set up my own style of waitqueue */
waiter.task = tsk;
waiter.type = RWSEM_WAITING_FOR_READ;
get_task_struct(tsk);
list_add_tail(&waiter.list, &sem->wait_list);
/* we don't need to touch the semaphore struct anymore */
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
/* wait to be given the lock */
for (;;) {
if (!waiter.task)
break;
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
tsk->state = TASK_RUNNING;
out:
;
}
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
int __down_read_trylock(struct rw_semaphore *sem)
{
unsigned long flags;
int ret = 0;
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity++;
ret = 1;
}
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
return ret;
}
/*
* get a write lock on the semaphore
*/
void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
{
struct rwsem_waiter waiter;
struct task_struct *tsk;
unsigned long flags;
raw_spin_lock_irqsave(&sem->wait_lock, flags);
/* set up my own style of waitqueue */
tsk = current;
waiter.task = tsk;
waiter.type = RWSEM_WAITING_FOR_WRITE;
list_add_tail(&waiter.list, &sem->wait_list);
/* wait for someone to release the lock */
for (;;) {
/*
* That is the key to support write lock stealing: allows the
* task already on CPU to get the lock soon rather than put
* itself into sleep and waiting for system woke it or someone
* else in the head of the wait list up.
*/
if (sem->activity == 0)
break;
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
schedule();
raw_spin_lock_irqsave(&sem->wait_lock, flags);
}
/* got the lock */
sem->activity = -1;
list_del(&waiter.list);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
}
void __sched __down_write(struct rw_semaphore *sem)
{
__down_write_nested(sem, 0);
}
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
int __down_write_trylock(struct rw_semaphore *sem)
{
unsigned long flags;
int ret = 0;
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->activity == 0) {
/* got the lock */
sem->activity = -1;
ret = 1;
}
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
return ret;
}
/*
* release a read lock on the semaphore
*/
void __up_read(struct rw_semaphore *sem)
{
unsigned long flags;
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (--sem->activity == 0 && !list_empty(&sem->wait_list))
sem = __rwsem_wake_one_writer(sem);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
}
/*
* release a write lock on the semaphore
*/
void __up_write(struct rw_semaphore *sem)
{
unsigned long flags;
raw_spin_lock_irqsave(&sem->wait_lock, flags);
sem->activity = 0;
if (!list_empty(&sem->wait_list))
sem = __rwsem_do_wake(sem, 1);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
}
/*
* downgrade a write lock into a read lock
* - just wake up any readers at the front of the queue
*/
void __downgrade_write(struct rw_semaphore *sem)
{
unsigned long flags;
raw_spin_lock_irqsave(&sem->wait_lock, flags);
sem->activity = 1;
if (!list_empty(&sem->wait_list))
sem = __rwsem_do_wake(sem, 0);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
}