[PATCH RFC 02/13] rwlock_t: Implement double_write_{,un}lock()

[Kirill Tkhai <ktkhai@odin.com>]

New helpers for locking two locks at a time.

Signed-off-by: Kirill Tkhai <ktkhai@odin.com>
---
 include/linux/spinlock.h |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 3e18379..e1e3054 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -426,4 +426,23 @@ extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
 #define atomic_dec_and_lock(atomic, lock) \
 		__cond_lock(lock, _atomic_dec_and_lock(atomic, lock))
 
+static inline void double_write_lock(rwlock_t *lock1, rwlock_t *lock2)
+{
+	if (lock1 < lock2) {
+		write_lock(lock1);
+		write_lock(lock2);
+	} else if (lock1 > lock2) {
+		write_lock(lock2);
+		write_lock(lock1);
+	} else {
+		write_lock(lock1);
+	}
+}
+static inline void double_write_unlock(rwlock_t *lock1, rwlock_t *lock2)
+{
+	if (lock2 != lock1)
+		write_unlock(lock2);
+	write_unlock(lock1);
+}
+
 #endif /* __LINUX_SPINLOCK_H */