[PATCH] read-write semaphore downgrade and trylock

Here's a patch from Christoph Hellwig and myself to supply write->read
semaphore downgrade, and also from Brian Watson to supply trylock for rwsems.

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index c74cc975cab6..320138d6643d 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -75,6 +75,16 @@ static inline void up_write(struct rw_semaphore *sem)
 	rwsemtrace(sem,"Leaving up_write");
 }
 
+/*
+ * downgrade write lock to read lock
+ */
+static inline void downgrade_write(struct rw_semaphore *sem)
+{
+	rwsemtrace(sem,"Entering downgrade_write");
+	__downgrade_write(sem);
+	rwsemtrace(sem,"Leaving downgrade_write");
+}
+
 
 #endif /* __KERNEL__ */
 #endif /* _LINUX_RWSEM_H */