[PATCH v2 1/5] locking: Add rwsem_assert_held() and rwsem_assert_held_write()

Matthew Wilcox (Oracle)
2023-10-07T20:36:06Z

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.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/rwbase_rt.h | 9 +++++++--
include/linux/rwsem.h | 42 ++++++++++++++++++++++++++++++++++-----
2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/include/linux/rwbase_rt.h b/include/linux/rwbase_rt.h
index 1d264dd08625..a04acd85705b 100644
--- a/include/linux/rwbase_rt.h
+++ b/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)
+{
+ BUG_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;
}
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 1dd530ce8b45..048149f781b3 100644
--- a/include/linux/rwsem.h
+++ b/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(const struct rw_semaphore *sem)
+{
+ WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE);
+}
+
+static inline void __rwsem_assert_held_write(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(const struct rw_semaphore *sem)
+{
+ BUG_ON(!rwsem_is_locked(sem));
+}
+
+static inline void __rwsem_assert_held_write(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 +189,18 @@ 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)
+{
+ lockdep_assert_held(sem);
+ __rwsem_assert_held(sem);
+}
+
+static inline void rwsem_assert_held_write(const struct rw_semaphore *sem)
+{
+ lockdep_assert_held_write(sem);
+ __rwsem_assert_held_write(sem);
+}
+
/*
* lock for reading
*/
--
2.40.1