/* * wait for a lock to be granted */ static inline struct rw_semaphore *rwsem_down_failed_common(struct rw_semaphore *sem, struct rwsem_waiter *waiter, signed long adjustment) { struct task_struct *tsk = current; signed long count; set_task_state(tsk,TASK_UNINTERRUPTIBLE); /* set up my own style of waitqueue */ spin_lock(&sem->wait_lock); waiter->task = tsk; list_add_tail(&waiter->list,&sem->wait_list); /* note that we're now waiting on the lock, but no longer actively read-locking */ count = rwsem_atomic_update(adjustment,sem); /* if there are no longer active locks, wake the front queued process(es) up * - it might even be this process, since the waker takes a more active part */ if (!(count & RWSEM_ACTIVE_MASK)) sem = __rwsem_do_wake(sem,1); 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; 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; }