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#include <sys/rwlock.h>
#ifdef DEBUG_SUBSYSTEM
#undef DEBUG_SUBSYSTEM
#endif
#define DEBUG_SUBSYSTEM S_RWLOCK
#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
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
};
/* wake a single writer */
static struct rw_semaphore *
__rwsem_wake_one_writer_locked(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;
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
return sem;
}
/* release a read lock on the semaphore */
static void
__up_read_locked(struct rw_semaphore *sem)
{
if (--sem->activity == 0 && !list_empty(&sem->wait_list))
sem = __rwsem_wake_one_writer_locked(sem);
}
/* trylock for writing -- returns 1 if successful, 0 if contention */
static int
__down_write_trylock_locked(struct rw_semaphore *sem)
{
int ret = 0;
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity = -1;
ret = 1;
}
return ret;
}
#endif
void
__rw_init(krwlock_t *rwlp, char *name, krw_type_t type, void *arg)
{
int flags = KM_SLEEP;
ASSERT(rwlp);
ASSERT(name);
ASSERT(type == RW_DEFAULT); /* XXX no irq handler use */
ASSERT(arg == NULL); /* XXX no irq handler use */
rwlp->rw_magic = RW_MAGIC;
rwlp->rw_owner = NULL;
rwlp->rw_name = NULL;
rwlp->rw_name_size = strlen(name) + 1;
/* We may be called when there is a non-zero preempt_count or
* interrupts are disabled is which case we must not sleep.
*/
if (current_thread_info()->preempt_count || irqs_disabled())
flags = KM_NOSLEEP;
rwlp->rw_name = kmem_alloc(rwlp->rw_name_size, flags);
if (rwlp->rw_name == NULL)
return;
init_rwsem(&rwlp->rw_sem);
strcpy(rwlp->rw_name, name);
}
EXPORT_SYMBOL(__rw_init);
void
__rw_destroy(krwlock_t *rwlp)
{
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
ASSERT(rwlp->rw_owner == NULL);
spin_lock(&rwlp->rw_sem.wait_lock);
ASSERT(list_empty(&rwlp->rw_sem.wait_list));
spin_unlock(&rwlp->rw_sem.wait_lock);
kmem_free(rwlp->rw_name, rwlp->rw_name_size);
memset(rwlp, RW_POISON, sizeof(krwlock_t));
}
EXPORT_SYMBOL(__rw_destroy);
/* Return 0 if the lock could not be obtained without blocking. */
int
__rw_tryenter(krwlock_t *rwlp, krw_t rw)
{
int rc = 0;
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
switch (rw) {
/* these functions return 1 if success, 0 if contention */
case RW_READER:
/* Here the Solaris code would return 0
* if there were any write waiters. Specifically
* thinking about the case where readers may have
* the lock and we would also allow this thread
* to grab the read lock with a writer waiting in the
* queue. This doesn't seem like a correctness
* issue, so just call down_read_trylock()
* for the test. We may have to revisit this if
* it becomes an issue */
rc = down_read_trylock(&rwlp->rw_sem);
break;
case RW_WRITER:
rc = down_write_trylock(&rwlp->rw_sem);
if (rc) {
/* there better not be anyone else
* holding the write lock here */
ASSERT(rwlp->rw_owner == NULL);
rwlp->rw_owner = current;
}
break;
default:
SBUG();
}
RETURN(rc);
}
EXPORT_SYMBOL(__rw_tryenter);
void
__rw_enter(krwlock_t *rwlp, krw_t rw)
{
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
switch (rw) {
case RW_READER:
/* Here the Solaris code would block
* if there were any write waiters. Specifically
* thinking about the case where readers may have
* the lock and we would also allow this thread
* to grab the read lock with a writer waiting in the
* queue. This doesn't seem like a correctness
* issue, so just call down_read()
* for the test. We may have to revisit this if
* it becomes an issue */
down_read(&rwlp->rw_sem);
break;
case RW_WRITER:
down_write(&rwlp->rw_sem);
/* there better not be anyone else
* holding the write lock here */
ASSERT(rwlp->rw_owner == NULL);
rwlp->rw_owner = current;
break;
default:
SBUG();
}
EXIT;
}
EXPORT_SYMBOL(__rw_enter);
void
__rw_exit(krwlock_t *rwlp)
{
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
/* rw_owner is held by current
* thread iff it is a writer */
if (rwlp->rw_owner == current) {
rwlp->rw_owner = NULL;
up_write(&rwlp->rw_sem);
} else {
up_read(&rwlp->rw_sem);
}
EXIT;
}
EXPORT_SYMBOL(__rw_exit);
void
__rw_downgrade(krwlock_t *rwlp)
{
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
ASSERT(rwlp->rw_owner == current);
rwlp->rw_owner = NULL;
downgrade_write(&rwlp->rw_sem);
EXIT;
}
EXPORT_SYMBOL(__rw_downgrade);
/* Return 0 if unable to perform the upgrade.
* Might be wise to fix the caller
* to acquire the write lock first?
*/
int
__rw_tryupgrade(krwlock_t *rwlp)
{
int rc = 0;
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
spin_lock(&rwlp->rw_sem.wait_lock);
/* Check if there is anyone waiting for the
* lock. If there is, then we know we should
* not try to upgrade the lock */
if (!list_empty(&rwlp->rw_sem.wait_list)) {
spin_unlock(&rwlp->rw_sem.wait_lock);
RETURN(0);
}
#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
/* Note that activity is protected by
* the wait_lock. Don't try to upgrade
* if there are multiple readers currently
* holding the lock */
if (rwlp->rw_sem.activity > 1) {
#else
/* Don't try to upgrade
* if there are multiple readers currently
* holding the lock */
if ((rwlp->rw_sem.count & RWSEM_ACTIVE_MASK) > 1) {
#endif
spin_unlock(&rwlp->rw_sem.wait_lock);
RETURN(0);
}
#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
/* Here it should be safe to drop the
* read lock and reacquire it for writing since
* we know there are no waiters */
__up_read_locked(&rwlp->rw_sem);
/* returns 1 if success, 0 if contention */
rc = __down_write_trylock_locked(&rwlp->rw_sem);
#else
/* Here it should be safe to drop the
* read lock and reacquire it for writing since
* we know there are no waiters */
up_read(&rwlp->rw_sem);
/* returns 1 if success, 0 if contention */
rc = down_write_trylock(&rwlp->rw_sem);
#endif
/* Check if upgrade failed. Should not ever happen
* if we got to this point */
ASSERT(rc);
ASSERT(rwlp->rw_owner == NULL);
rwlp->rw_owner = current;
spin_unlock(&rwlp->rw_sem.wait_lock);
RETURN(1);
}
EXPORT_SYMBOL(__rw_tryupgrade);
kthread_t *
__rw_owner(krwlock_t *rwlp)
{
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
RETURN(rwlp->rw_owner);
}
EXPORT_SYMBOL(__rw_owner);
int
__rw_read_held(krwlock_t *rwlp)
{
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
RETURN(__rw_lock_held(rwlp) && rwlp->rw_owner == NULL);
}
EXPORT_SYMBOL(__rw_read_held);
int
__rw_write_held(krwlock_t *rwlp)
{
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
RETURN(rwlp->rw_owner == current);
}
EXPORT_SYMBOL(__rw_write_held);
int
__rw_lock_held(krwlock_t *rwlp)
{
int rc = 0;
ENTRY;
ASSERT(rwlp);
ASSERT(rwlp->rw_magic == RW_MAGIC);
spin_lock_irq(&(rwlp->rw_sem.wait_lock));
#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
if (rwlp->rw_sem.activity != 0) {
#else
if (rwlp->rw_sem.count != 0) {
#endif
rc = 1;
}
spin_unlock_irq(&(rwlp->rw_sem.wait_lock));
RETURN(rc);
}
EXPORT_SYMBOL(__rw_lock_held);
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