diff options
| -rw-r--r-- | lib/rwsem.c | 72 |
1 files changed, 57 insertions, 15 deletions
diff --git a/lib/rwsem.c b/lib/rwsem.c index 4063645..fb658af 100644 --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -178,12 +178,12 @@ try_again_write: } /* - * wait for a lock to be granted + * wait for the read lock to be granted */ -static struct rw_semaphore __sched * -rwsem_down_failed_common(struct rw_semaphore *sem, - enum rwsem_waiter_type type, signed long adjustment) +struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) { + enum rwsem_waiter_type type = RWSEM_WAITING_FOR_READ; + signed long adjustment = -RWSEM_ACTIVE_READ_BIAS; struct rwsem_waiter waiter; struct task_struct *tsk = current; signed long count; @@ -238,21 +238,63 @@ rwsem_down_failed_common(struct rw_semaphore *sem, } /* - * wait for the read lock to be granted - */ -struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) -{ - return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_READ, - -RWSEM_ACTIVE_READ_BIAS); -} - -/* * wait for the write lock to be granted */ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) { - return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_WRITE, - -RWSEM_ACTIVE_WRITE_BIAS); + enum rwsem_waiter_type type = RWSEM_WAITING_FOR_WRITE; + signed long adjustment = -RWSEM_ACTIVE_WRITE_BIAS; + struct rwsem_waiter waiter; + struct task_struct *tsk = current; + signed long count; + + /* set up my own style of waitqueue */ + waiter.task = tsk; + waiter.type = type; + get_task_struct(tsk); + + raw_spin_lock_irq(&sem->wait_lock); + if (list_empty(&sem->wait_list)) + adjustment += RWSEM_WAITING_BIAS; + list_add_tail(&waiter.list, &sem->wait_list); + + /* we're now waiting on the lock, but no longer actively locking */ + count = rwsem_atomic_update(adjustment, sem); + + /* If there are no active locks, wake the front queued process(es) up. + * + * Alternatively, if we're called from a failed down_write(), there + * were already threads queued before us and there are no active + * writers, the lock must be read owned; so we try to wake any read + * locks that were queued ahead of us. */ + if (count == RWSEM_WAITING_BIAS) + sem = __rwsem_do_wake(sem, RWSEM_WAKE_NO_ACTIVE); + else if (count > RWSEM_WAITING_BIAS && + adjustment == -RWSEM_ACTIVE_WRITE_BIAS) + sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED); + + raw_spin_unlock_irq(&sem->wait_lock); + + /* wait to be given the lock */ + while (true) { + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + if (!waiter.task) + break; + + raw_spin_lock_irq(&sem->wait_lock); + /* Try to get the writer sem, may steal from the head writer: */ + if (type == RWSEM_WAITING_FOR_WRITE) + if (try_get_writer_sem(sem, &waiter)) { + raw_spin_unlock_irq(&sem->wait_lock); + return sem; + } + raw_spin_unlock_irq(&sem->wait_lock); + schedule(); + } + + tsk->state = TASK_RUNNING; + + return sem; } /* |