From cba04135c05ef740116b1cb9c598281ea9d3c71c Mon Sep 17 00:00:00 2001
From: Michel Lespinasse <walken@google.com>
Date: Tue, 7 May 2013 06:45:51 -0700
Subject: [PATCH] --- yaml --- r: 373747 b: refs/heads/master c:
 1e78277ccbbb48af32a618d1ef0e8534e0b648d7 h: refs/heads/master i:   373745:
 edfa4998265ebe1f3d1bdf9b31ea51ebdc352eff   373743:
 297d6e05d83ab97376fcdecc5d2516dd29dcd4fd v: v3

---
 [refs]            |  2 +-
 trunk/lib/rwsem.c | 72 +++++++++++++++++++++++++++++++++++++----------
 2 files changed, 58 insertions(+), 16 deletions(-)

diff --git a/[refs] b/[refs]
index 45488050a94d..f677616bcc2f 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: f7dd1cee9a4e2b1450e4a3732636dfbf28562ee4
+refs/heads/master: 1e78277ccbbb48af32a618d1ef0e8534e0b648d7
diff --git a/trunk/lib/rwsem.c b/trunk/lib/rwsem.c
index 40636454cf3c..fb658af1c12c 100644
--- a/trunk/lib/rwsem.c
+++ b/trunk/lib/rwsem.c
@@ -178,12 +178,12 @@ static int try_get_writer_sem(struct rw_semaphore *sem,
 }
 
 /*
- * 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;
@@ -237,22 +237,64 @@ rwsem_down_failed_common(struct rw_semaphore *sem,
 	return 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;
 }
 
 /*