locking: Add rwsem_assert_held() and rwsem_assert_held_write()

Modelled after lockdep_assert_held() and lockdep_assert_held_write(),
but are always active, even when lockdep is disabled.  Of course, they
don't test that _this_ thread is the owner, but it's sufficient to catch
many bugs and doesn't incur the same performance penalty as lockdep.
Acked-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

include/linux/rwbase_rt.h

@@ -26,12 +26,17 @@ struct rwbase_rt {
 	} while (0)
 
 
-static __always_inline bool rw_base_is_locked(struct rwbase_rt *rwb)
+static __always_inline bool rw_base_is_locked(const struct rwbase_rt *rwb)
 {
 	return atomic_read(&rwb->readers) != READER_BIAS;
 }
 
-static __always_inline bool rw_base_is_contended(struct rwbase_rt *rwb)
+static inline void rw_base_assert_held_write(const struct rwbase_rt *rwb)
+{
+	WARN_ON(atomic_read(&rwb->readers) != WRITER_BIAS);
+}
+
+static __always_inline bool rw_base_is_contended(const struct rwbase_rt *rwb)
 {
 	return atomic_read(&rwb->readers) > 0;
 }

include/linux/rwsem.h

@@ -66,14 +66,24 @@ struct rw_semaphore {
 #endif
 };
 
-/* In all implementations count != 0 means locked */
+#define RWSEM_UNLOCKED_VALUE		0UL
+#define RWSEM_WRITER_LOCKED		(1UL << 0)
+#define __RWSEM_COUNT_INIT(name)	.count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
+
 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 {
-	return atomic_long_read(&sem->count) != 0;
+	return atomic_long_read(&sem->count) != RWSEM_UNLOCKED_VALUE;
 }
 
-#define RWSEM_UNLOCKED_VALUE		0L
-#define __RWSEM_COUNT_INIT(name)	.count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
+static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
+{
+	WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE);
+}
+
+static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
+{
+	WARN_ON(!(atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED));
+}
 
 /* Common initializer macros and functions */
 
@@ -152,11 +162,21 @@ do {								\
 	__init_rwsem((sem), #sem, &__key);			\
 } while (0)
 
-static __always_inline int rwsem_is_locked(struct rw_semaphore *sem)
+static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem)
 {
 	return rw_base_is_locked(&sem->rwbase);
 }
 
+static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
+{
+	WARN_ON(!rwsem_is_locked(sem));
+}
+
+static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
+{
+	rw_base_assert_held_write(sem);
+}
+
 static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
 {
 	return rw_base_is_contended(&sem->rwbase);
@@ -169,6 +189,22 @@ static __always_inline int rwsem_is_contended(struct rw_semaphore *sem)
  * the RT specific variant.
  */
 
+static inline void rwsem_assert_held(const struct rw_semaphore *sem)
+{
+	if (IS_ENABLED(CONFIG_LOCKDEP))
+		lockdep_assert_held(sem);
+	else
+		rwsem_assert_held_nolockdep(sem);
+}
+
+static inline void rwsem_assert_held_write(const struct rw_semaphore *sem)
+{
+	if (IS_ENABLED(CONFIG_LOCKDEP))
+		lockdep_assert_held_write(sem);
+	else
+		rwsem_assert_held_write_nolockdep(sem);
+}
+
 /*
  * lock for reading
  */