From 5683a1144eb2f647800e2b505aaabd4e6edfa155 Mon Sep 17 00:00:00 2001
From: Con Kolivas <kernel@kolivas.org>
Date: Sun, 29 Sep 2013 15:14:06 +1000
Subject: [PATCH] Provide a function to downgrade a cglock from a write lock to
 an intermediate variant.

---
 miner.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/miner.h b/miner.h
index d945740e..60eb7516 100644
--- a/miner.h
+++ b/miner.h
@@ -843,7 +843,7 @@ static inline void cglock_init(cglock_t *lock)
 	rwlock_init(&lock->rwlock);
 }
 
-/* Read lock variant of cglock */
+/* Read lock variant of cglock. Cannot be promoted. */
 static inline void cg_rlock(cglock_t *lock)
 {
 	mutex_lock(&lock->mutex);
@@ -851,7 +851,8 @@ static inline void cg_rlock(cglock_t *lock)
 	mutex_unlock_noyield(&lock->mutex);
 }
 
-/* Intermediate variant of cglock */
+/* Intermediate variant of cglock - behaves as a read lock but can be promoted
+ * to a write lock or demoted to read lock. */
 static inline void cg_ilock(cglock_t *lock)
 {
 	mutex_lock(&lock->mutex);
@@ -878,6 +879,12 @@ static inline void cg_dwlock(cglock_t *lock)
 	mutex_unlock_noyield(&lock->mutex);
 }
 
+/* Demote a write variant to an intermediate variant */
+static inline void cg_dwilock(cglock_t *lock)
+{
+	wr_unlock(&lock->rwlock);
+}
+
 /* Downgrade intermediate variant to a read lock */
 static inline void cg_dlock(cglock_t *lock)
 {