Re: [PATCH v2] locking/rtmutex: Annotate API and implementation

[Bart Van Assche]

On 5/6/26 9:35 AM, Sebastian Andrzej Siewior wrote:
> Hmm. This mostly reassembles __mutex_lock() from mutex.c which does the
> same thing. Couldn't we get away doing the same thing meaning a
> __cond_acquires() on those with a return value and a __acquire() in the
> void case? I think it would make sense to keep those two close in terms
> of annotations.

Please take a look at the rt_mutex_lock() changes in the diff below.

Thanks,

Bart.

diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
index 78e7e588817c..9e1f012f89db 100644
--- a/include/linux/rtmutex.h
+++ b/include/linux/rtmutex.h
@@ -56,6 +56,8 @@ static inline struct task_struct 
*rt_mutex_owner(struct rt_mutex_base *lock)
 #endif
 extern void rt_mutex_base_init(struct rt_mutex_base *rtb);

+context_lock_struct(rt_mutex);
+
 /**
  * The rt_mutex structure
  *
@@ -108,8 +110,10 @@ do { \
 extern void __rt_mutex_init(struct rt_mutex *lock, const char *name, 
struct lock_class_key *key);

 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-extern void rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int 
subclass);
-extern void _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct 
lockdep_map *nest_lock);
+extern void rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int 
subclass)
+	__acquires(lock);
+extern void _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct 
lockdep_map *nest_lock)
+	__acquires(lock);
 #define rt_mutex_lock(lock) rt_mutex_lock_nested(lock, 0)
 #define rt_mutex_lock_nest_lock(lock, nest_lock)			\
 	do {								\
@@ -118,15 +122,19 @@ extern void _rt_mutex_lock_nest_lock(struct 
rt_mutex *lock, struct lockdep_map *
 	} while (0)

 #else
-extern void rt_mutex_lock(struct rt_mutex *lock);
+extern void rt_mutex_lock(struct rt_mutex *lock) __acquires(lock);
 #define rt_mutex_lock_nested(lock, subclass) rt_mutex_lock(lock)
 #define rt_mutex_lock_nest_lock(lock, nest_lock) rt_mutex_lock(lock)
 #endif

-extern int rt_mutex_lock_interruptible(struct rt_mutex *lock);
-extern int rt_mutex_lock_killable(struct rt_mutex *lock);
-extern int rt_mutex_trylock(struct rt_mutex *lock);
+extern int rt_mutex_lock_interruptible(struct rt_mutex *lock)
+	__cond_acquires(0, lock);
+extern int rt_mutex_lock_killable(struct rt_mutex *lock)
+	__cond_acquires(0, lock);
+extern int rt_mutex_trylock(struct rt_mutex *lock)
+	__cond_acquires(true, lock);

-extern void rt_mutex_unlock(struct rt_mutex *lock);
+extern void rt_mutex_unlock(struct rt_mutex *lock)
+	__releases(lock);

 #endif
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 4f386ea6c792..69759fde7d10 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -484,6 +484,7 @@ static __always_inline bool __waiter_less(struct 
rb_node *a, const struct rb_nod

 static __always_inline void
 rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter 
*waiter)
+	__must_hold(&lock->wait_lock)
 {
 	lockdep_assert_held(&lock->wait_lock);

@@ -492,6 +493,7 @@ rt_mutex_enqueue(struct rt_mutex_base *lock, struct 
rt_mutex_waiter *waiter)

 static __always_inline void
 rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter 
*waiter)
+	__must_hold(&lock->wait_lock)
 {
 	lockdep_assert_held(&lock->wait_lock);

@@ -1092,6 +1094,7 @@ static int __sched 
rt_mutex_adjust_prio_chain(struct task_struct *task,
 static int __sched
 try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
 		     struct rt_mutex_waiter *waiter)
+	__must_hold(&lock->wait_lock)
 {
 	lockdep_assert_held(&lock->wait_lock);

@@ -1319,6 +1322,7 @@ static int __sched task_blocks_on_rt_mutex(struct 
rt_mutex_base *lock,
  */
 static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
 					    struct rt_mutex_base *lock)
+	__must_hold(&lock->wait_lock)
 {
 	struct rt_mutex_waiter *waiter;

@@ -1479,6 +1483,7 @@ static void __sched rt_mutex_slowunlock(struct 
rt_mutex_base *lock)
 }

 static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
+	__no_context_analysis
 {
 	if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
 		return;
diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c
index 124219aea46e..f9345fa22286 100644
--- a/kernel/locking/rtmutex_api.c
+++ b/kernel/locking/rtmutex_api.c
@@ -41,6 +41,7 @@ static __always_inline int 
__rt_mutex_lock_common(struct rt_mutex *lock,
 						  unsigned int state,
 						  struct lockdep_map *nest_lock,
 						  unsigned int subclass)
+	__cond_acquires(0, lock)
 {
 	int ret;

@@ -67,13 +68,19 @@ EXPORT_SYMBOL(rt_mutex_base_init);
  */
 void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int 
subclass)
 {
-	__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, subclass);
+	if (__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, subclass) 
== 0)
+		return;
+	WARN_ON_ONCE(true);
+	__acquire(lock); /* to keep the compiler happy */
 }
 EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);

 void __sched _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct 
lockdep_map *nest_lock)
 {
-	__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, nest_lock, 0);
+	if (__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, nest_lock, 0) == 0)
+		return;
+	WARN_ON_ONCE(true);
+	__acquire(lock); /* to keep the compiler happy */
 }
 EXPORT_SYMBOL_GPL(_rt_mutex_lock_nest_lock);

@@ -86,7 +93,10 @@ EXPORT_SYMBOL_GPL(_rt_mutex_lock_nest_lock);
  */
 void __sched rt_mutex_lock(struct rt_mutex *lock)
 {
-	__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, 0);
+	if (__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, 0) == 0)
+		return;
+	WARN_ON_ONCE(true);
+	__acquire(lock); /* to keep the compiler happy */
 }
 EXPORT_SYMBOL_GPL(rt_mutex_lock);
 #endif
@@ -157,6 +167,7 @@ void __sched rt_mutex_unlock(struct rt_mutex *lock)
 {
 	mutex_release(&lock->dep_map, _RET_IP_);
 	__rt_mutex_unlock(&lock->rtmutex);
+	__release(lock);
 }
 EXPORT_SYMBOL_GPL(rt_mutex_unlock);

@@ -182,6 +193,7 @@ int __sched __rt_mutex_futex_trylock(struct 
rt_mutex_base *lock)
  */
 bool __sched __rt_mutex_futex_unlock(struct rt_mutex_base *lock,
 				     struct rt_wake_q_head *wqh)
+	__must_hold(&lock->wait_lock)
 {
 	lockdep_assert_held(&lock->wait_lock);

@@ -312,6 +324,7 @@ int __sched __rt_mutex_start_proxy_lock(struct 
rt_mutex_base *lock,
 					struct rt_mutex_waiter *waiter,
 					struct task_struct *task,
 					struct wake_q_head *wake_q)
+	__must_hold(&lock->wait_lock)
 {
 	int ret;