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

[Bart Van Assche <bvanassche@acm.org>]

On 5/4/26 11:39 AM, Peter Zijlstra wrote:
> This does not build, I need at least the below, but then PREEMPT_RT is
> still not happy.
Apparently I had tested my patch with PREEMPT_RT=n only. The patch below
should support both PREEMPT_RT=n and PREEMPT_RT=y:

---
  include/linux/rtmutex.h      | 22 +++++++++++++++-------
  kernel/locking/Makefile      |  1 +
  kernel/locking/rtmutex.c     |  5 +++++
  kernel/locking/rtmutex_api.c |  6 ++++++
  4 files changed, 27 insertions(+), 7 deletions(-)

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/Makefile b/kernel/locking/Makefile
index cee1901d4cff..24dc00e12aa6 100644
--- a/kernel/locking/Makefile
+++ b/kernel/locking/Makefile
@@ -4,6 +4,7 @@
  KCOV_INSTRUMENT		:= n

  CONTEXT_ANALYSIS_mutex.o := y
+CONTEXT_ANALYSIS_rtmutex.o := y
  CONTEXT_ANALYSIS_rtmutex_api.o := y
  CONTEXT_ANALYSIS_ww_rt_mutex.o := y
  CONTEXT_ANALYSIS_rwsem.o := y
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..23ad997ddd65 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;

@@ -66,12 +67,14 @@ EXPORT_SYMBOL(rt_mutex_base_init);
   * @subclass: the lockdep subclass
   */
  void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int 
subclass)
+	__no_context_analysis /* ignoring the return value below is fine in 
this case */
  {
  	__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, subclass);
  }
  EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);

  void __sched _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct 
lockdep_map *nest_lock)
+	__no_context_analysis /* ignoring the return value below is fine in 
this case */
  {
  	__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, nest_lock, 0);
  }
@@ -157,6 +160,7 @@ 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 +186,7 @@ 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 +317,7 @@ 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;