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From 956dcc483ffd16f99561df6b1eef993e989789b2 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 14 Sep 2009 19:01:21 +0200
Subject: [PATCH] rt: Fix rwlocks/rwsem rt_[down_]read_trylock()
commit 00261a9426ed50016e07cbef028578e93589761c in tip.
rt_read_trylock() and rt_down_read_trylock() take the lock / semaphore
unconditionally when it is write locked. Check read_depth if current
owns the lock. If it's 0 we know it is write locked and return 0.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
kernel/rt.c | 13 ++++++++++++-
1 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/kernel/rt.c b/kernel/rt.c
index 710cef5..fd033a9 100644
--- a/kernel/rt.c
+++ b/kernel/rt.c
@@ -204,10 +204,14 @@ int __lockfunc rt_read_trylock(rwlock_t *rwlock)
int ret = 1;
/*
- * recursive read locks succeed when current owns the lock
+ * recursive read locks succeed when current owns the lock,
+ * but not when read_depth == 0 which means that the lock is
+ * write locked.
*/
if (rt_mutex_real_owner(lock) != current)
ret = rt_mutex_trylock(lock);
+ else if (!rwlock->read_depth)
+ ret = 0;
if (ret) {
rwlock->read_depth++;
@@ -348,8 +352,15 @@ 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_real_owner(lock) != current)
ret = rt_mutex_trylock(&rwsem->lock);
+ else if (!rwsem->read_depth)
+ ret = 0;
if (ret) {
rwsem->read_depth++;
--
1.7.0.4
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