/*
* 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 */
smp_mb();
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;
smp_mb();
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;
}
/*
* wait for the write lock to be granted
*/
struct rw_semaphore fastcall *rwsem_down_write_failed(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
rwsemtrace(sem,"Entering rwsem_down_write_failed");
waiter.flags = RWSEM_WAITING_FOR_WRITE;
rwsem_down_failed_common(sem,&waiter,-RWSEM_ACTIVE_BIAS);
rwsemtrace(sem,"Leaving rwsem_down_write_failed");
return sem;
}
/*
* release a read lock on the semaphore
*/
void fastcall __up_read(struct rw_semaphore *sem)
{
rwsemtrace(sem,"Entering __up_read");
spin_lock(&sem->wait_lock);
if (--sem->activity==0 && !list_empty(&sem->wait_list))
sem = __rwsem_wake_one_writer(sem);
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __up_read");
}
/*
* release a write lock on the semaphore
*/
void fastcall __up_write(struct rw_semaphore *sem)
{
rwsemtrace(sem,"Entering __up_write");
spin_lock(&sem->wait_lock);
sem->activity = 0;
if (!list_empty(&sem->wait_list))
sem = __rwsem_do_wake(sem);
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __up_write");
}
/*
* wait for the read lock to be granted
*/
struct rw_semaphore fastcall __sched *
rwsem_down_read_failed(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
rwsemtrace(sem, "Entering rwsem_down_read_failed");
waiter.flags = RWSEM_WAITING_FOR_READ;
rwsem_down_failed_common(sem, &waiter,
RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS);
rwsemtrace(sem, "Leaving rwsem_down_read_failed");
return sem;
}
/*
* 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");
}
/*
* downgrade a write lock into a read lock
* - caller incremented waiting part of count and discovered it still negative
* - just wake up any readers at the front of the queue
*/
struct rw_semaphore fastcall *rwsem_downgrade_wake(struct rw_semaphore *sem)
{
rwsemtrace(sem, "Entering rwsem_downgrade_wake");
spin_lock(&sem->wait_lock);
/* do nothing if list empty */
if (!list_empty(&sem->wait_list))
sem = __rwsem_do_wake(sem, 1);
spin_unlock(&sem->wait_lock);
rwsemtrace(sem, "Leaving rwsem_downgrade_wake");
return sem;
}
/*
* 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");
}
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
int __down_write_trylock(struct rw_semaphore *sem)
{
int ret = 0;
rwsemtrace(sem,"Entering __down_write_trylock");
spin_lock(&sem->wait_lock);
if (sem->activity==0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity = -1;
ret = 1;
}
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __down_write_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;
unsigned long flags;
rwsemtrace(sem, "Entering __down_write");
spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity = -1;
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.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_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:
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;
}
/*
* get a read lock on the semaphore
*/
void __down_read(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
struct task_struct *tsk;
rwsemtrace(sem,"Entering __down_read");
spin_lock(&sem->wait_lock);
if (sem->activity>=0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity++;
spin_unlock(&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;
list_add_tail(&waiter.list,&sem->wait_list);
/* we don't need to touch the semaphore struct anymore */
spin_unlock(&sem->wait_lock);
/* wait to be given the lock */
for (;;) {
if (!waiter.flags)
break;
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
tsk->state = TASK_RUNNING;
out:
rwsemtrace(sem,"Leaving __down_read");
}
/*
* handle the lock being released whilst there are 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 flags zeroised
*/
static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem)
{
struct rwsem_waiter *waiter;
int woken;
rwsemtrace(sem,"Entering __rwsem_do_wake");
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
/* 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);
waiter->flags = 0;
wake_up_process(waiter->task);
goto out;
}
/* grant an infinite number of read locks to the readers at the front of the queue */
woken = 0;
do {
list_del(&waiter->list);
waiter->flags = 0;
wake_up_process(waiter->task);
woken++;
if (list_empty(&sem->wait_list))
break;
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
} while (waiter->flags&RWSEM_WAITING_FOR_READ);
sem->activity += woken;
out:
rwsemtrace(sem,"Leaving __rwsem_do_wake");
return sem;
}
/*
* handle the lock release when processes blocked on it that can now run
* - if we come here from up_xxxx(), then:
* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
* - there must be someone on the queue
* - 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 downgrading is false
*/
static inline struct rw_semaphore *
__rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
{
struct rwsem_waiter *waiter;
struct task_struct *tsk;
struct list_head *next;
signed long oldcount, woken, loop;
rwsemtrace(sem, "Entering __rwsem_do_wake");
if (downgrading)
goto dont_wake_writers;
/* if we came through an up_xxxx() call, we only only wake someone up
* if we can transition the active part of the count from 0 -> 1
*/
try_again:
oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS, sem)
- RWSEM_ACTIVE_BIAS;
if (oldcount & RWSEM_ACTIVE_MASK)
goto undo;
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
/* try to grant a single write lock if there's a writer at the front
* of the queue - note we leave the 'active part' of the count
* incremented by 1 and the waiting part incremented by 0x00010000
*/
if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
goto readers_only;
/* We must be careful not to touch 'waiter' after we set ->task = NULL.
* It is an allocated on the waiter's stack and may become invalid at
* any time after that point (due to a wakeup from another source).
*/
list_del(&waiter->list);
tsk = waiter->task;
mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
goto out;
/* don't want to wake any writers */
dont_wake_writers:
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
goto out;
/* grant an infinite number of read locks to the readers at the front
* of the queue
* - note we increment the 'active part' of the count by the number of
* readers before waking any processes up
*/
readers_only:
woken = 0;
do {
woken++;
if (waiter->list.next == &sem->wait_list)
break;
waiter = list_entry(waiter->list.next,
struct rwsem_waiter, list);
} while (waiter->flags & RWSEM_WAITING_FOR_READ);
loop = woken;
woken *= RWSEM_ACTIVE_BIAS - RWSEM_WAITING_BIAS;
if (!downgrading)
/* we'd already done one increment earlier */
woken -= RWSEM_ACTIVE_BIAS;
rwsem_atomic_add(woken, sem);
next = sem->wait_list.next;
for (; loop > 0; loop--) {
waiter = list_entry(next, struct rwsem_waiter, list);
next = waiter->list.next;
tsk = waiter->task;
mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
}
sem->wait_list.next = next;
next->prev = &sem->wait_list;
out:
rwsemtrace(sem, "Leaving __rwsem_do_wake");
return sem;
/* undo the change to count, but check for a transition 1->0 */
undo:
if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) != 0)
goto out;
goto try_again;
}
/*
* handle the lock being released whilst there are processes blocked on it that can now run
* - if we come here, then:
* - the 'active part' of the count (&0x0000ffff) reached zero but has been re-incremented
* - the 'waiting part' of the count (&0xffff0000) is negative (and will still be so)
* - there must be someone on the queue
* - the spinlock must be held by the caller
* - woken process blocks are discarded from the list after having flags zeroised
* - 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 list_head *next;
signed long oldcount;
int woken, loop;
rwsemtrace(sem,"Entering __rwsem_do_wake");
if (!wakewrite)
goto dont_wake_writers;
/* only wake someone up if we can transition the active part of the count from 0 -> 1 */
try_again:
oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS,sem) - RWSEM_ACTIVE_BIAS;
if (oldcount & RWSEM_ACTIVE_MASK)
goto undo;
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
/* try to grant a single write lock if there's a writer at the front of the queue
* - note we leave the 'active part' of the count incremented by 1 and the waiting part
* incremented by 0x00010000
*/
if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
goto readers_only;
list_del(&waiter->list);
waiter->flags = 0;
wake_up_process(waiter->task);
goto out;
/* don't want to wake any writers */
dont_wake_writers:
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
goto out;
/* grant an infinite number of read locks to the readers at the front of the queue
* - note we increment the 'active part' of the count by the number of readers (less one
* for the activity decrement we've already done) before waking any processes up
*/
readers_only:
woken = 0;
do {
woken++;
if (waiter->list.next==&sem->wait_list)
break;
waiter = list_entry(waiter->list.next,struct rwsem_waiter,list);
} while (waiter->flags & RWSEM_WAITING_FOR_READ);
loop = woken;
woken *= RWSEM_ACTIVE_BIAS-RWSEM_WAITING_BIAS;
woken -= RWSEM_ACTIVE_BIAS;
rwsem_atomic_add(woken,sem);
next = sem->wait_list.next;
for (; loop>0; loop--) {
waiter = list_entry(next,struct rwsem_waiter,list);
next = waiter->list.next;
waiter->flags = 0;
wake_up_process(waiter->task);
}
sem->wait_list.next = next;
next->prev = &sem->wait_list;
out:
rwsemtrace(sem,"Leaving __rwsem_do_wake");
return sem;
/* undo the change to count, but check for a transition 1->0 */
undo:
if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS,sem)!=0)
goto out;
goto try_again;
}
