locking/ww_mutex: Support Clang's context analysis

Add support for Clang's context analysis for ww_mutex.

The programming model for ww_mutex is subtly more complex than other
locking primitives when using ww_acquire_ctx. Encoding the respective
pre-conditions for ww_mutex lock/unlock based on ww_acquire_ctx state
using Clang's context analysis makes incorrect use of the API harder.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-21-elver@google.com

1 files changed, 16 insertions, 6 deletions

diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 45ff6f7a872b..58e959ee10e9 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -44,7 +44,7 @@ struct ww_class {
 	unsigned int is_wait_die;
 };
 
-struct ww_mutex {
+context_lock_struct(ww_mutex) {
 	struct WW_MUTEX_BASE base;
 	struct ww_acquire_ctx *ctx;
 #ifdef DEBUG_WW_MUTEXES
@@ -52,7 +52,7 @@ struct ww_mutex {
 #endif
 };
 
-struct ww_acquire_ctx {
+context_lock_struct(ww_acquire_ctx) {
 	struct task_struct *task;
 	unsigned long stamp;
 	unsigned int acquired;
@@ -107,6 +107,7 @@ struct ww_acquire_ctx {
  */
 static inline void ww_mutex_init(struct ww_mutex *lock,
 				 struct ww_class *ww_class)
+	__assumes_ctx_lock(lock)
 {
 	ww_mutex_base_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
 	lock->ctx = NULL;
@@ -141,6 +142,7 @@ static inline void ww_mutex_init(struct ww_mutex *lock,
  */
 static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 				   struct ww_class *ww_class)
+	__acquires(ctx) __no_context_analysis
 {
 	ctx->task = current;
 	ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
@@ -179,6 +181,7 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
  * data structures.
  */
 static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
+	__releases(ctx) __acquires_shared(ctx) __no_context_analysis
 {
 #ifdef DEBUG_WW_MUTEXES
 	lockdep_assert_held(ctx);
@@ -196,6 +199,7 @@ static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
  * mutexes have been released with ww_mutex_unlock.
  */
 static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
+	__releases_shared(ctx) __no_context_analysis
 {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	mutex_release(&ctx->first_lock_dep_map, _THIS_IP_);
@@ -245,7 +249,8 @@ static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
  *
  * A mutex acquired with this function must be released with ww_mutex_unlock.
  */
-extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
+extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+	__cond_acquires(0, lock) __must_hold(ctx);
 
 /**
  * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
@@ -278,7 +283,8 @@ extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acq
  * A mutex acquired with this function must be released with ww_mutex_unlock.
  */
 extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
-						    struct ww_acquire_ctx *ctx);
+						    struct ww_acquire_ctx *ctx)
+	__cond_acquires(0, lock) __must_hold(ctx);
 
 /**
  * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
@@ -305,6 +311,7 @@ extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
  */
 static inline void
 ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+	__acquires(lock) __must_hold(ctx) __no_context_analysis
 {
 	int ret;
 #ifdef DEBUG_WW_MUTEXES
@@ -342,6 +349,7 @@ ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 static inline int __must_check
 ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 				 struct ww_acquire_ctx *ctx)
+	__cond_acquires(0, lock) __must_hold(ctx)
 {
 #ifdef DEBUG_WW_MUTEXES
 	DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
@@ -349,10 +357,11 @@ ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 	return ww_mutex_lock_interruptible(lock, ctx);
 }
 
-extern void ww_mutex_unlock(struct ww_mutex *lock);
+extern void ww_mutex_unlock(struct ww_mutex *lock) __releases(lock);
 
 extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,
-					 struct ww_acquire_ctx *ctx);
+					 struct ww_acquire_ctx *ctx)
+	__cond_acquires(true, lock) __must_hold(ctx);
 
 /***
  * ww_mutex_destroy - mark a w/w mutex unusable
@@ -363,6 +372,7 @@ extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,
  * this function is called.
  */
 static inline void ww_mutex_destroy(struct ww_mutex *lock)
+	__must_not_hold(lock)
 {
 #ifndef CONFIG_PREEMPT_RT
 	mutex_destroy(&lock->base);