[RFC 1/2] refcount: add __cond_lock() for conditional lock refcount API

[Alexander Aring]

This patch adds the __cond_lock() macro to refcounts conditional lock
API. Currently sparse cannot detect the conditional lock handling of
refcount_dec_and_lock() functionality and prints a context imbalance
warning like:

warning: context imbalance in 'put_rsb' - unexpected unlock

with this patch and having the refcount_dec_and_lock() functionality
inside the if condition to decide whenever doing unlock or not the
warning disappears.

The patch follows a similar naming scheme like raw_spin_trylock() by
adding a "raw_" prefix to refcount_dec_and_lock() functionality and
introduce a macro for the replaced functions that uses __cond_lock()
to signal that an acquire depends on the return value of the passed
function.

A cast to bool seems to be necessary because __cond_lock() does return a
non-boolean scalar type.

The __must_check annotation was tested and is still working with this
patch applied.

Signed-off-by: Alexander Aring <aahringo@xxxxxxxxxx>
---
 include/linux/refcount.h | 21 ++++++++++++++++-----
 lib/refcount.c           | 23 ++++++++++++-----------
 2 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index b8a6e387f8f9..be7b970ce475 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -361,9 +361,20 @@ static inline void refcount_dec(refcount_t *r)
 
 extern __must_check bool refcount_dec_if_one(refcount_t *r);
 extern __must_check bool refcount_dec_not_one(refcount_t *r);
-extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock);
-extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock);
-extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r,
-						       spinlock_t *lock,
-						       unsigned long *flags);
+extern __must_check bool raw_refcount_dec_and_mutex_lock(refcount_t *r,
+							 struct mutex *lock);
+#define refcount_dec_and_mutex_lock(r, lock) \
+	((bool)(__cond_lock(lock, raw_refcount_dec_and_mutex_lock(r, lock))))
+
+extern __must_check bool raw_refcount_dec_and_lock(refcount_t *r,
+						   spinlock_t *lock);
+#define refcount_dec_and_lock(r, lock) \
+	((bool)(__cond_lock(lock, raw_refcount_dec_and_lock(r, lock))))
+
+extern __must_check bool raw_refcount_dec_and_lock_irqsave(refcount_t *r,
+							   spinlock_t *lock,
+							   unsigned long *flags);
+#define refcount_dec_and_lock_irqsave(r, lock, flags) \
+	((bool)(__cond_lock(lock, raw_refcount_dec_and_lock_irqsave(r, lock, flags))))
+
 #endif /* _LINUX_REFCOUNT_H */
diff --git a/lib/refcount.c b/lib/refcount.c
index a207a8f22b3c..1a8c7b9aba23 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -110,7 +110,7 @@ EXPORT_SYMBOL(refcount_dec_not_one);
  * Return: true and hold mutex if able to decrement refcount to 0, false
  *         otherwise
  */
-bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
+bool raw_refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
 {
 	if (refcount_dec_not_one(r))
 		return false;
@@ -123,11 +123,11 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
 
 	return true;
 }
-EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
+EXPORT_SYMBOL(raw_refcount_dec_and_mutex_lock);
 
 /**
- * refcount_dec_and_lock - return holding spinlock if able to decrement
- *                         refcount to 0
+ * raw_refcount_dec_and_lock - return holding spinlock if able to decrement
+ *			       refcount to 0
  * @r: the refcount
  * @lock: the spinlock to be locked
  *
@@ -141,7 +141,7 @@ EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
  * Return: true and hold spinlock if able to decrement refcount to 0, false
  *         otherwise
  */
-bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
+bool raw_refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
 {
 	if (refcount_dec_not_one(r))
 		return false;
@@ -154,11 +154,12 @@ bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
 
 	return true;
 }
-EXPORT_SYMBOL(refcount_dec_and_lock);
+EXPORT_SYMBOL(raw_refcount_dec_and_lock);
 
 /**
- * refcount_dec_and_lock_irqsave - return holding spinlock with disabled
- *                                 interrupts if able to decrement refcount to 0
+ * raw_refcount_dec_and_lock_irqsave - return holding spinlock with disabled
+ *				       interrupts if able to decrement
+ *				       refcount to 0
  * @r: the refcount
  * @lock: the spinlock to be locked
  * @flags: saved IRQ-flags if the is acquired
@@ -169,8 +170,8 @@ EXPORT_SYMBOL(refcount_dec_and_lock);
  * Return: true and hold spinlock if able to decrement refcount to 0, false
  *         otherwise
  */
-bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
-				   unsigned long *flags)
+bool raw_refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
+				       unsigned long *flags)
 {
 	if (refcount_dec_not_one(r))
 		return false;
@@ -183,4 +184,4 @@ bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,
 
 	return true;
 }
-EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);
+EXPORT_SYMBOL(raw_refcount_dec_and_lock_irqsave);
-- 
2.31.1