2005-04-16 15:20:36 -07:00
|
|
|
/* 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/module.h>
|
|
|
|
|
|
|
|
struct rwsem_waiter {
|
|
|
|
struct list_head list;
|
|
|
|
struct task_struct *task;
|
|
|
|
unsigned int flags;
|
|
|
|
#define RWSEM_WAITING_FOR_READ 0x00000001
|
|
|
|
#define RWSEM_WAITING_FOR_WRITE 0x00000002
|
|
|
|
};
|
|
|
|
|
|
|
|
#if RWSEM_DEBUG
|
|
|
|
void rwsemtrace(struct rw_semaphore *sem, const char *str)
|
|
|
|
{
|
|
|
|
if (sem->debug)
|
|
|
|
printk("[%d] %s({%d,%d})\n",
|
|
|
|
current->pid, str, sem->activity,
|
|
|
|
list_empty(&sem->wait_list) ? 0 : 1);
|
|
|
|
}
|
|
|
|
#endif
|
|
|
|
|
|
|
|
/*
|
|
|
|
* initialise the semaphore
|
|
|
|
*/
|
|
|
|
void fastcall init_rwsem(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
sem->activity = 0;
|
|
|
|
spin_lock_init(&sem->wait_lock);
|
|
|
|
INIT_LIST_HEAD(&sem->wait_list);
|
|
|
|
#if RWSEM_DEBUG
|
|
|
|
sem->debug = 0;
|
|
|
|
#endif
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* 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;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __rwsem_do_wake");
|
|
|
|
|
|
|
|
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
|
|
|
|
|
|
|
|
if (!wakewrite) {
|
|
|
|
if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
|
|
|
|
goto out;
|
|
|
|
goto dont_wake_writers;
|
|
|
|
}
|
|
|
|
|
|
|
|
/* if we are allowed to wake writers try to grant a single write lock
|
|
|
|
* if there's a writer at the front of the queue
|
|
|
|
* - we leave the 'waiting count' incremented to signify potential
|
|
|
|
* contention
|
|
|
|
*/
|
|
|
|
if (waiter->flags & RWSEM_WAITING_FOR_WRITE) {
|
|
|
|
sem->activity = -1;
|
|
|
|
list_del(&waiter->list);
|
|
|
|
tsk = waiter->task;
|
|
|
|
/* Don't touch waiter after ->task has been NULLed */
|
2005-05-01 08:58:47 -07:00
|
|
|
smp_mb();
|
2005-04-16 15:20:36 -07:00
|
|
|
waiter->task = NULL;
|
|
|
|
wake_up_process(tsk);
|
|
|
|
put_task_struct(tsk);
|
|
|
|
goto out;
|
|
|
|
}
|
|
|
|
|
|
|
|
/* grant an infinite number of read locks to the front of the queue */
|
|
|
|
dont_wake_writers:
|
|
|
|
woken = 0;
|
|
|
|
while (waiter->flags & RWSEM_WAITING_FOR_READ) {
|
|
|
|
struct list_head *next = waiter->list.next;
|
|
|
|
|
|
|
|
list_del(&waiter->list);
|
|
|
|
tsk = waiter->task;
|
2005-05-01 08:58:47 -07:00
|
|
|
smp_mb();
|
2005-04-16 15:20:36 -07:00
|
|
|
waiter->task = NULL;
|
|
|
|
wake_up_process(tsk);
|
|
|
|
put_task_struct(tsk);
|
|
|
|
woken++;
|
|
|
|
if (list_empty(&sem->wait_list))
|
|
|
|
break;
|
|
|
|
waiter = list_entry(next, struct rwsem_waiter, list);
|
|
|
|
}
|
|
|
|
|
|
|
|
sem->activity += woken;
|
|
|
|
|
|
|
|
out:
|
|
|
|
rwsemtrace(sem, "Leaving __rwsem_do_wake");
|
|
|
|
return sem;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* wake a single writer
|
|
|
|
*/
|
|
|
|
static inline struct rw_semaphore *
|
|
|
|
__rwsem_wake_one_writer(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
struct rwsem_waiter *waiter;
|
|
|
|
struct task_struct *tsk;
|
|
|
|
|
|
|
|
sem->activity = -1;
|
|
|
|
|
|
|
|
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
|
|
|
|
list_del(&waiter->list);
|
|
|
|
|
|
|
|
tsk = waiter->task;
|
2005-05-01 08:58:47 -07:00
|
|
|
smp_mb();
|
2005-04-16 15:20:36 -07:00
|
|
|
waiter->task = NULL;
|
|
|
|
wake_up_process(tsk);
|
|
|
|
put_task_struct(tsk);
|
|
|
|
return sem;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* get a read lock on the semaphore
|
|
|
|
*/
|
|
|
|
void fastcall __sched __down_read(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
struct rwsem_waiter waiter;
|
|
|
|
struct task_struct *tsk;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __down_read");
|
|
|
|
|
|
|
|
spin_lock_irq(&sem->wait_lock);
|
|
|
|
|
|
|
|
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
|
|
|
|
/* granted */
|
|
|
|
sem->activity++;
|
|
|
|
spin_unlock_irq(&sem->wait_lock);
|
|
|
|
goto out;
|
|
|
|
}
|
|
|
|
|
|
|
|
tsk = current;
|
|
|
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
|
|
|
|
|
|
/* set up my own style of waitqueue */
|
|
|
|
waiter.task = tsk;
|
|
|
|
waiter.flags = 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 */
|
|
|
|
spin_unlock_irq(&sem->wait_lock);
|
|
|
|
|
|
|
|
/* wait to be given the lock */
|
|
|
|
for (;;) {
|
|
|
|
if (!waiter.task)
|
|
|
|
break;
|
|
|
|
schedule();
|
|
|
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
|
|
}
|
|
|
|
|
|
|
|
tsk->state = TASK_RUNNING;
|
|
|
|
|
|
|
|
out:
|
|
|
|
rwsemtrace(sem, "Leaving __down_read");
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* trylock for reading -- returns 1 if successful, 0 if contention
|
|
|
|
*/
|
|
|
|
int fastcall __down_read_trylock(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
unsigned long flags;
|
|
|
|
int ret = 0;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __down_read_trylock");
|
|
|
|
|
|
|
|
spin_lock_irqsave(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
|
|
|
|
/* granted */
|
|
|
|
sem->activity++;
|
|
|
|
ret = 1;
|
|
|
|
}
|
|
|
|
|
|
|
|
spin_unlock_irqrestore(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Leaving __down_read_trylock");
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* get a write lock on the semaphore
|
|
|
|
* - we increment the waiting count anyway to indicate an exclusive lock
|
|
|
|
*/
|
|
|
|
void fastcall __sched __down_write(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
struct rwsem_waiter waiter;
|
|
|
|
struct task_struct *tsk;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __down_write");
|
|
|
|
|
|
|
|
spin_lock_irq(&sem->wait_lock);
|
|
|
|
|
|
|
|
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
|
|
|
|
/* granted */
|
|
|
|
sem->activity = -1;
|
|
|
|
spin_unlock_irq(&sem->wait_lock);
|
|
|
|
goto out;
|
|
|
|
}
|
|
|
|
|
|
|
|
tsk = current;
|
|
|
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
|
|
|
|
|
|
/* set up my own style of waitqueue */
|
|
|
|
waiter.task = tsk;
|
|
|
|
waiter.flags = RWSEM_WAITING_FOR_WRITE;
|
|
|
|
get_task_struct(tsk);
|
|
|
|
|
|
|
|
list_add_tail(&waiter.list, &sem->wait_list);
|
|
|
|
|
|
|
|
/* we don't need to touch the semaphore struct anymore */
|
|
|
|
spin_unlock_irq(&sem->wait_lock);
|
|
|
|
|
|
|
|
/* wait to be given the lock */
|
|
|
|
for (;;) {
|
|
|
|
if (!waiter.task)
|
|
|
|
break;
|
|
|
|
schedule();
|
|
|
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
|
|
}
|
|
|
|
|
|
|
|
tsk->state = TASK_RUNNING;
|
|
|
|
|
|
|
|
out:
|
|
|
|
rwsemtrace(sem, "Leaving __down_write");
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* trylock for writing -- returns 1 if successful, 0 if contention
|
|
|
|
*/
|
|
|
|
int fastcall __down_write_trylock(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
unsigned long flags;
|
|
|
|
int ret = 0;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __down_write_trylock");
|
|
|
|
|
|
|
|
spin_lock_irqsave(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
|
|
|
|
/* granted */
|
|
|
|
sem->activity = -1;
|
|
|
|
ret = 1;
|
|
|
|
}
|
|
|
|
|
|
|
|
spin_unlock_irqrestore(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Leaving __down_write_trylock");
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* release a read lock on the semaphore
|
|
|
|
*/
|
|
|
|
void fastcall __up_read(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
unsigned long flags;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __up_read");
|
|
|
|
|
|
|
|
spin_lock_irqsave(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
if (--sem->activity == 0 && !list_empty(&sem->wait_list))
|
|
|
|
sem = __rwsem_wake_one_writer(sem);
|
|
|
|
|
|
|
|
spin_unlock_irqrestore(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Leaving __up_read");
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* release a write lock on the semaphore
|
|
|
|
*/
|
|
|
|
void fastcall __up_write(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
unsigned long flags;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __up_write");
|
|
|
|
|
|
|
|
spin_lock_irqsave(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
sem->activity = 0;
|
|
|
|
if (!list_empty(&sem->wait_list))
|
|
|
|
sem = __rwsem_do_wake(sem, 1);
|
|
|
|
|
|
|
|
spin_unlock_irqrestore(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Leaving __up_write");
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* downgrade a write lock into a read lock
|
|
|
|
* - just wake up any readers at the front of the queue
|
|
|
|
*/
|
|
|
|
void fastcall __downgrade_write(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
unsigned long flags;
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Entering __downgrade_write");
|
|
|
|
|
|
|
|
spin_lock_irqsave(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
sem->activity = 1;
|
|
|
|
if (!list_empty(&sem->wait_list))
|
|
|
|
sem = __rwsem_do_wake(sem, 0);
|
|
|
|
|
|
|
|
spin_unlock_irqrestore(&sem->wait_lock, flags);
|
|
|
|
|
|
|
|
rwsemtrace(sem, "Leaving __downgrade_write");
|
|
|
|
}
|
|
|
|
|
|
|
|
EXPORT_SYMBOL(init_rwsem);
|
|
|
|
EXPORT_SYMBOL(__down_read);
|
|
|
|
EXPORT_SYMBOL(__down_read_trylock);
|
|
|
|
EXPORT_SYMBOL(__down_write);
|
|
|
|
EXPORT_SYMBOL(__down_write_trylock);
|
|
|
|
EXPORT_SYMBOL(__up_read);
|
|
|
|
EXPORT_SYMBOL(__up_write);
|
|
|
|
EXPORT_SYMBOL(__downgrade_write);
|
|
|
|
#if RWSEM_DEBUG
|
|
|
|
EXPORT_SYMBOL(rwsemtrace);
|
|
|
|
#endif
|