rt: Fix rwlocks/rwsem rt_[down_]read_trylock()

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>

1 files changed, 12 insertions, 1 deletions

diff --git a/kernel/rt.c b/kernel/rt.c
index 710cef59ee8a..fd033a9bd7c2 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++;