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

Bart Van Assche
2026-05-04T11:56:23Z

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;