The readers of mainline rwsems are not allowed to nest, the rwsems in the
PREEMPT_RT kernel should not nest either.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/rwsem_rt.h |    1 -
 kernel/rt.c              |   37 ++++++++-----------------------------
 2 files changed, 8 insertions(+), 30 deletions(-)

Index: linux-3.12.15-rt25-r1s8/include/linux/rwsem_rt.h
===================================================================
--- linux-3.12.15-rt25-r1s8.orig/include/linux/rwsem_rt.h
+++ linux-3.12.15-rt25-r1s8/include/linux/rwsem_rt.h
@@ -20,7 +20,6 @@
 
 struct rw_semaphore {
 	struct rt_mutex		lock;
-	int			read_depth;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
Index: linux-3.12.15-rt25-r1s8/kernel/rt.c
===================================================================
--- linux-3.12.15-rt25-r1s8.orig/kernel/rt.c
+++ linux-3.12.15-rt25-r1s8/kernel/rt.c
@@ -320,10 +320,8 @@ EXPORT_SYMBOL(rt_up_write);
 
 void  rt_up_read(struct rw_semaphore *rwsem)
 {
-	if (--rwsem->read_depth == 0) {
-		rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
-		rt_mutex_unlock(&rwsem->lock);
-	}
+	rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
+	rt_mutex_unlock(&rwsem->lock);
 }
 EXPORT_SYMBOL(rt_up_read);
 
@@ -334,7 +332,6 @@ EXPORT_SYMBOL(rt_up_read);
 void  rt_downgrade_write(struct rw_semaphore *rwsem)
 {
 	BUG_ON(rt_mutex_owner(&rwsem->lock) != current);
-	rwsem->read_depth = 1;
 }
 EXPORT_SYMBOL(rt_downgrade_write);
 
@@ -371,37 +368,20 @@ void rt_down_write_nested_lock(struct rw
 
 int  rt_down_read_trylock(struct rw_semaphore *rwsem)
 {
-	struct rt_mutex *lock = &rwsem->lock;
-	int ret = 1;
-
-	/*
-	 * recursive read locks succeed when current owns the rwsem,
-	 * but not when read_depth == 0 which means that the rwsem is
-	 * write locked.
-	 */
-	if (rt_mutex_owner(lock) != current) {
-		ret = rt_mutex_trylock(&rwsem->lock);
-		if (ret)
-			rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
-	} else if (!rwsem->read_depth) {
-		ret = 0;
-	}
+	int ret;
 
+	ret = rt_mutex_trylock(&rwsem->lock);
 	if (ret)
-		rwsem->read_depth++;
+		rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
+
 	return ret;
 }
 EXPORT_SYMBOL(rt_down_read_trylock);
 
 static void __rt_down_read(struct rw_semaphore *rwsem, int subclass)
 {
-	struct rt_mutex *lock = &rwsem->lock;
-
-	if (rt_mutex_owner(lock) != current) {
-		rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_);
-		rt_mutex_lock(&rwsem->lock);
-	}
-	rwsem->read_depth++;
+	rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_);
+	rt_mutex_lock(&rwsem->lock);
 }
 
 void  rt_down_read(struct rw_semaphore *rwsem)
@@ -426,7 +406,6 @@ void  __rt_rwsem_init(struct rw_semaphor
 	debug_check_no_locks_freed((void *)rwsem, sizeof(*rwsem));
 	lockdep_init_map(&rwsem->dep_map, name, key, 0);
 #endif
-	rwsem->read_depth = 0;
 	rwsem->lock.save_state = 0;
 }
 EXPORT_SYMBOL(__rt_rwsem_init);