diff options
-rw-r--r-- | lib/rwsem-spinlock.c | 23 | ||||
-rw-r--r-- | lib/rwsem.c | 26 |
2 files changed, 19 insertions, 30 deletions
diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c index 5f117f3..9be8a91 100644 --- a/lib/rwsem-spinlock.c +++ b/lib/rwsem-spinlock.c @@ -70,26 +70,17 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); - if (!wakewrite) { - if (waiter->type == RWSEM_WAITING_FOR_WRITE) - goto out; - goto dont_wake_writers; - } - - /* - * as we support write lock stealing, we can't set sem->activity - * to -1 here to indicate we get the lock. Instead, we wake it up - * to let it go get it again. - */ if (waiter->type == RWSEM_WAITING_FOR_WRITE) { - wake_up_process(waiter->task); + if (wakewrite) + /* Wake up a writer. Note that we do not grant it the + * lock - it will have to acquire it when it runs. */ + wake_up_process(waiter->task); goto out; } /* grant an infinite number of read locks to the front of the queue */ - dont_wake_writers: woken = 0; - while (waiter->type == RWSEM_WAITING_FOR_READ) { + do { struct list_head *next = waiter->list.next; list_del(&waiter->list); @@ -99,10 +90,10 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) wake_up_process(tsk); put_task_struct(tsk); woken++; - if (list_empty(&sem->wait_list)) + if (next == &sem->wait_list) break; waiter = list_entry(next, struct rwsem_waiter, list); - } + } while (waiter->type != RWSEM_WAITING_FOR_WRITE); sem->activity += woken; diff --git a/lib/rwsem.c b/lib/rwsem.c index 0d50e46..9a675fa 100644 --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -68,20 +68,17 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type) signed long woken, loop, adjustment; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); - if (waiter->type != RWSEM_WAITING_FOR_WRITE) - goto readers_only; - - if (wake_type == RWSEM_WAKE_READ_OWNED) - /* Another active reader was observed, so wakeup is not - * likely to succeed. Save the atomic op. - */ + if (waiter->type == RWSEM_WAITING_FOR_WRITE) { + if (wake_type != RWSEM_WAKE_READ_OWNED) + /* Wake writer at the front of the queue, but do not + * grant it the lock yet as we want other writers + * to be able to steal it. Readers, on the other hand, + * will block as they will notice the queued writer. + */ + wake_up_process(waiter->task); goto out; + } - /* Wake up the writing waiter and let the task grab the sem: */ - wake_up_process(waiter->task); - goto out; - - readers_only: /* If we come here from up_xxxx(), another thread might have reached * rwsem_down_failed_common() before we acquired the spinlock and * woken up a waiter, making it now active. We prefer to check for @@ -125,7 +122,8 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type) rwsem_atomic_add(adjustment, sem); next = sem->wait_list.next; - for (loop = woken; loop > 0; loop--) { + loop = woken; + do { waiter = list_entry(next, struct rwsem_waiter, list); next = waiter->list.next; tsk = waiter->task; @@ -133,7 +131,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type) waiter->task = NULL; wake_up_process(tsk); put_task_struct(tsk); - } + } while (--loop); sem->wait_list.next = next; next->prev = &sem->wait_list; |