| From 00261a9426ed50016e07cbef028578e93589761c 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> |
| |
| 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++; |
| -- |
| 1.7.1.1 |
| |
