rt-locks-fix-recursive-rwlocks-and-cleanup-rwsems.patch

From 4981ddc6409d8d10def1644e99823dc18d55daa9 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 3 Jul 2009 13:16:24 -0500
Subject: [PATCH] rt-locks: fix recursive rwlocks and cleanup rwsems

commit 4981ddc6409d8d10def1644e99823dc18d55daa9 in tip.

recursive rwlocks are only allowed for recursive reads.  recursive
rwsems are not allowed at all.

Follow up to Jan Blunks fix.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/rt.c b/kernel/rt.c
index d095969..df30930 100644
--- a/kernel/rt.c
+++ b/kernel/rt.c
@@ -201,24 +201,18 @@ EXPORT_SYMBOL(rt_write_trylock_irqsave);
 int __lockfunc rt_read_trylock(rwlock_t *rwlock)
 {
 	struct rt_mutex *lock = &rwlock->lock;
-	unsigned long flags;
-	int ret;
+	int ret = 1;
 
 	/*
-	 * Read locks within the self-held write lock succeed.
+	 * recursive read locks succeed when current owns the lock
 	 */
-	spin_lock_irqsave(&lock->wait_lock, flags);
-	if (rt_mutex_real_owner(lock) == current) {
-		spin_unlock_irqrestore(&lock->wait_lock, flags);
+	if (rt_mutex_real_owner(lock) != current || !rwlock->read_depth)
+		ret = rt_mutex_trylock(lock);
+
+	if (ret) {
 		rwlock->read_depth++;
 		rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
-		return 1;
 	}
-	spin_unlock_irqrestore(&lock->wait_lock, flags);
-
-	ret = rt_mutex_trylock(lock);
-	if (ret)
-		rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
 
 	return ret;
 }
@@ -233,21 +227,16 @@ EXPORT_SYMBOL(rt_write_lock);
 
 void __lockfunc rt_read_lock(rwlock_t *rwlock)
 {
-	unsigned long flags;
 	struct rt_mutex *lock = &rwlock->lock;
 
 	rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
+
 	/*
-	 * Read locks within the write lock succeed.
+	 * recursive read locks succeed when current owns the lock
 	 */
-	spin_lock_irqsave(&lock->wait_lock, flags);
-	if (rt_mutex_real_owner(lock) == current) {
-		spin_unlock_irqrestore(&lock->wait_lock, flags);
-		rwlock->read_depth++;
-		return;
-	}
-	spin_unlock_irqrestore(&lock->wait_lock, flags);
-	__rt_spin_lock(lock);
+	if (rt_mutex_real_owner(lock) != current || !rwlock->read_depth)
+		__rt_spin_lock(lock);
+	rwlock->read_depth++;
 }
 
 EXPORT_SYMBOL(rt_read_lock);
@@ -262,22 +251,13 @@ EXPORT_SYMBOL(rt_write_unlock);
 
 void __lockfunc rt_read_unlock(rwlock_t *rwlock)
 {
-	struct rt_mutex *lock = &rwlock->lock;
-	unsigned long flags;
-
 	rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
-	// TRACE_WARN_ON(lock->save_state != 1);
-	/*
-	 * Read locks within the self-held write lock succeed.
-	 */
-	spin_lock_irqsave(&lock->wait_lock, flags);
-	if (rt_mutex_real_owner(lock) == current && rwlock->read_depth) {
-		spin_unlock_irqrestore(&lock->wait_lock, flags);
-		rwlock->read_depth--;
-		return;
-	}
-	spin_unlock_irqrestore(&lock->wait_lock, flags);
-	__rt_spin_unlock(&rwlock->lock);
+
+	BUG_ON(rwlock->read_depth <= 0);
+
+	/* Release the lock only when read_depth is down to 0 */
+	if (--rwlock->read_depth == 0)
+		__rt_spin_unlock(&rwlock->lock);
 }
 EXPORT_SYMBOL(rt_read_unlock);
 
@@ -324,19 +304,7 @@ EXPORT_SYMBOL(rt_up_write);
 
 void  rt_up_read(struct rw_semaphore *rwsem)
 {
-	unsigned long flags;
-
 	rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
-	/*
-	 * Read locks within the self-held write lock succeed.
-	 */
-	spin_lock_irqsave(&rwsem->lock.wait_lock, flags);
-	if (rt_mutex_real_owner(&rwsem->lock) == current && rwsem->read_depth) {
-		spin_unlock_irqrestore(&rwsem->lock.wait_lock, flags);
-		rwsem->read_depth--;
-		return;
-	}
-	spin_unlock_irqrestore(&rwsem->lock.wait_lock, flags);
 	rt_mutex_unlock(&rwsem->lock);
 }
 EXPORT_SYMBOL(rt_up_read);
@@ -377,10 +345,8 @@ EXPORT_SYMBOL(rt_down_write_nested);
 
 int  rt_down_read_trylock(struct rw_semaphore *rwsem)
 {
-	unsigned long flags;
-	int ret;
+	int ret = rt_mutex_trylock(&rwsem->lock);
 
-	ret = rt_mutex_trylock(&rwsem->lock);
 	if (ret)
 		rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
 	return ret;
@@ -389,21 +355,7 @@ EXPORT_SYMBOL(rt_down_read_trylock);
 
 static void __rt_down_read(struct rw_semaphore *rwsem, int subclass)
 {
-	unsigned long flags;
-
 	rwsem_acquire_read(&rwsem->dep_map, subclass, 0, _RET_IP_);
-
-	/*
-	 * Read locks within the write lock succeed.
-	 */
-	spin_lock_irqsave(&rwsem->lock.wait_lock, flags);
-
-	if (rt_mutex_real_owner(&rwsem->lock) == current) {
-		spin_unlock_irqrestore(&rwsem->lock.wait_lock, flags);
-		rwsem->read_depth++;
-		return;
-	}
-	spin_unlock_irqrestore(&rwsem->lock.wait_lock, flags);
 	rt_mutex_lock(&rwsem->lock);
 }
 
@@ -430,7 +382,6 @@ void  __rt_rwsem_init(struct rw_semaphore *rwsem, char *name,
 	lockdep_init_map(&rwsem->dep_map, name, key, 0);
 #endif
 	__rt_mutex_init(&rwsem->lock, name);
-	rwsem->read_depth = 0;
 }
 EXPORT_SYMBOL(__rt_rwsem_init);
 
-- 
1.7.1.1