Remove the rwsem_down_failed_common function and replace it with two
identical copies of its code in rwsem_down_{read,write}_failed.
This is because we want to make different optimizations in
rwsem_down_{read,write}_failed; we are adding this pure-duplication
step as a separate commit in order to make it easier to check the
following steps.
Signed-off-by: Michel Lespinasse <wal...@google.com>
---
lib/rwsem.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 57 insertions(+), 15 deletions(-)
diff --git a/lib/rwsem.c b/lib/rwsem.c
index 40636454cf3c..fb658af1c12c 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;
}
/*
--
1.8.1.3
--
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