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

Commit Message

Matthew Wilcox Oct. 7, 2023, 8:35 p.m. UTC

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) <[e-mail]>
---
 include/linux/rwbase_rt.h |  9 +++++++--
 include/linux/rwsem.h     | 42 ++++++++++++++++++++++++++++++++++-----
 2 files changed, 44 insertions(+), 7 deletions(-)

Comments

Dave Chinner Oct. 8, 2023, 9:54 p.m. UTC | #1

On Sat, Oct 07, 2023 at 09:35:39PM +0100, Matthew Wilcox (Oracle) wrote:
> 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) <[e-mail]>
> ---
.....
> @@ -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);
> +}

	if (IS_ENABLED(CONFIG_LOCKDEP))
		lockdep_assert_held(sem);
	else
		__rwsem_assert_held(sem);

-Dave.

Patch

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
  */