Change DEFINE_SEMAPHORE() to take a number argument

Fundamentally semaphores are a counted primitive, but
DEFINE_SEMAPHORE() does not expose this and explicitly creates a
binary semaphore.

Change DEFINE_SEMAPHORE() to take a number argument and use that in the
few places that open-coded it using __SEMAPHORE_INITIALIZER().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[mcgrof: add some tribal knowledge about why some folks prefer
 binary sempahores over mutexes]
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h
index 6694d0019a68..04655faadc2d 100644
--- a/include/linux/semaphore.h
+++ b/include/linux/semaphore.h
@@ -25,8 +25,14 @@ struct semaphore {
 	.wait_list	= LIST_HEAD_INIT((name).wait_list),		\
 }
 
-#define DEFINE_SEMAPHORE(name)	\
-	struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1)
+/*
+ * Unlike mutexes, binary semaphores do not have an owner, so up() can
+ * be called in a different thread from the one which called down().
+ * It is also safe to call down_trylock() and up() from interrupt
+ * context.
+ */
+#define DEFINE_SEMAPHORE(_name, _n)	\
+	struct semaphore _name = __SEMAPHORE_INITIALIZER(_name, _n)
 
 static inline void sema_init(struct semaphore *sem, int val)
 {