/*
* Routine: convert_port_to_locked_task
* Purpose:
* Internal helper routine to convert from a port to a locked
* task. Used by several routines that try to convert from a
* task port to a reference on some task related object.
* Conditions:
* Nothing locked, blocking OK.
*/
task_t
convert_port_to_locked_task(ipc_port_t port)
{
int try_failed_count = 0;
while (IP_VALID(port)) {
task_t task;
ip_lock(port);
if (!ip_active(port) || (ip_kotype(port) != IKOT_TASK)) {
ip_unlock(port);
return TASK_NULL;
}
task = (task_t) port->ip_kobject;
assert(task != TASK_NULL);
/*
* Normal lock ordering puts task_lock() before ip_lock().
* Attempt out-of-order locking here.
*/
if (task_lock_try(task)) {
ip_unlock(port);
return(task);
}
try_failed_count++;
ip_unlock(port);
mutex_pause(try_failed_count);
}
return TASK_NULL;
}
/*
* Routine: semaphore_dereference
*
* Release a reference on a semaphore. If this is the last reference,
* the semaphore data structure is deallocated.
*/
void
semaphore_dereference(
semaphore_t semaphore)
{
uint32_t collisions;
spl_t spl_level;
if (semaphore == NULL)
return;
if (hw_atomic_sub(&semaphore->ref_count, 1) != 0)
return;
/*
* Last ref, clean up the port [if any]
* associated with the semaphore, destroy
* it (if still active) and then free
* the semaphore.
*/
ipc_port_t port = semaphore->port;
if (IP_VALID(port)) {
assert(!port->ip_srights);
ipc_port_dealloc_kernel(port);
}
/*
* Lock the semaphore to lock in the owner task reference.
* Then continue to try to lock the task (inverse order).
*/
spl_level = splsched();
semaphore_lock(semaphore);
for (collisions = 0; semaphore->active; collisions++) {
task_t task = semaphore->owner;
assert(task != TASK_NULL);
if (task_lock_try(task)) {
semaphore_destroy_internal(task, semaphore);
/* semaphore unlocked */
splx(spl_level);
task_unlock(task);
goto out;
}
/* failed to get out-of-order locks */
semaphore_unlock(semaphore);
splx(spl_level);
mutex_pause(collisions);
spl_level = splsched();
semaphore_lock(semaphore);
}
semaphore_unlock(semaphore);
splx(spl_level);
out:
zfree(semaphore_zone, semaphore);
}
