locking/mutex: Redo __mutex_init() to reduce generated code size

mutex_init() invokes __mutex_init() providing the name of the lock and
a pointer to a the lock class. With LOCKDEP enabled this information is
useful but without LOCKDEP it not used at all. Passing the pointer
information of the lock class might be considered negligible but the
name of the lock is passed as well and the string is stored. This
information is wasting storage.

Split __mutex_init() into a _genereic() variant doing the initialisation
of the lock and a _lockdep() version which does _genereic() plus the
lockdep bits. Restrict the lockdep version to lockdep enabled builds
allowing the compiler to remove the unused parameter.

This results in the following size reduction:

        text     data       bss        dec  filename
  | 30237599  8161430   1176624   39575653  vmlinux.defconfig
  | 3023326  8149142   1176560   39558971  vmlinux.defconfig.patched
     -4.2KiB   -12KiB

  | 32455099  8471098  12934684   53860881  vmlinux.defconfig.lockdep
  | 32455100  8471098  12934684   53860882  vmlinux.defconfig.patched.lockdep

  | 27152407  7191822   2068040   3641226  vmlinux.defconfig.preempt_rt
  | 27145937  7183630   2067976   36397543  vmlinux.defconfig.patched.preempt_rt
     -6.3KiB    -8KiB

  | 29382020  7505742  13784608   50672370  vmlinux.defconfig.preempt_rt.lockdep
  | 29376229  7505742  13784544   50666515  vmlinux.defconfig.patched.preempt_rt.lockdep
     -5.6KiB

[peterz: folded fix from boqun]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/20251125145425.68319-1-boqun.feng@gmail.com
Link: https://patch.msgid.link/20251105142350.Tfeevs2N@linutronix.de

Author: Sebastian Andrzej Siewior

include/linux/mutex.h

@@ -86,8 +86,23 @@ do {									\
 #define DEFINE_MUTEX(mutexname) \
 	struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 
-extern void __mutex_init(struct mutex *lock, const char *name,
-			 struct lock_class_key *key);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+void mutex_init_lockep(struct mutex *lock, const char *name, struct lock_class_key *key);
+
+static inline void __mutex_init(struct mutex *lock, const char *name,
+				struct lock_class_key *key)
+{
+	mutex_init_lockep(lock, name, key);
+}
+#else
+extern void mutex_init_generic(struct mutex *lock);
+
+static inline void __mutex_init(struct mutex *lock, const char *name,
+				struct lock_class_key *key)
+{
+	mutex_init_generic(lock);
+}
+#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
 
 /**
  * mutex_is_locked - is the mutex locked
@@ -111,17 +126,27 @@ extern bool mutex_is_locked(struct mutex *lock);
 #define DEFINE_MUTEX(mutexname)						\
 	struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 
-extern void __mutex_rt_init(struct mutex *lock, const char *name,
-			    struct lock_class_key *key);
-
 #define mutex_is_locked(l)	rt_mutex_base_is_locked(&(l)->rtmutex)
 
-#define __mutex_init(mutex, name, key)			\
-do {							\
-	rt_mutex_base_init(&(mutex)->rtmutex);		\
-	__mutex_rt_init((mutex), name, key);		\
-} while (0)
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern void mutex_rt_init_lockdep(struct mutex *mutex, const char *name,
+			     struct lock_class_key *key);
+
+static inline void __mutex_init(struct mutex *lock, const char *name,
+				struct lock_class_key *key)
+{
+	mutex_rt_init_lockdep(lock, name, key);
+}
 
+#else
+extern void mutex_rt_init_generic(struct mutex *mutex);
+
+static inline void __mutex_init(struct mutex *lock, const char *name,
+				struct lock_class_key *key)
+{
+	mutex_rt_init_generic(lock);
+}
+#endif /* !CONFIG_LOCKDEP */
 #endif /* CONFIG_PREEMPT_RT */
 
 #ifdef CONFIG_DEBUG_MUTEXES

kernel/locking/mutex-debug.c

@@ -78,16 +78,8 @@ void debug_mutex_unlock(struct mutex *lock)
 	}
 }
 
-void debug_mutex_init(struct mutex *lock, const char *name,
-		      struct lock_class_key *key)
+void debug_mutex_init(struct mutex *lock)
 {
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	/*
-	 * Make sure we are not reinitializing a held lock:
-	 */
-	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
-	lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_SLEEP);
-#endif
 	lock->magic = lock;
 }
 

kernel/locking/mutex.c

@@ -43,19 +43,16 @@
 # define MUTEX_WARN_ON(cond)
 #endif
 
-void
-__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
+static void __mutex_init_generic(struct mutex *lock)
 {
 	atomic_long_set(&lock->owner, 0);
 	raw_spin_lock_init(&lock->wait_lock);
 	INIT_LIST_HEAD(&lock->wait_list);
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 	osq_lock_init(&lock->osq);
 #endif
-
-	debug_mutex_init(lock, name, key);
+	debug_mutex_init(lock);
 }
-EXPORT_SYMBOL(__mutex_init);
 
 static inline struct task_struct *__owner_task(unsigned long owner)
 {
@@ -142,6 +139,11 @@ static inline bool __mutex_trylock(struct mutex *lock)
  * There is nothing that would stop spreading the lockdep annotations outwards
  * except more code.
  */
+void mutex_init_generic(struct mutex *lock)
+{
+	__mutex_init_generic(lock);
+}
+EXPORT_SYMBOL(mutex_init_generic);
 
 /*
  * Optimistic trylock that only works in the uncontended case. Make sure to
@@ -166,7 +168,21 @@ static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
 
 	return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
 }
-#endif
+
+#else /* !CONFIG_DEBUG_LOCK_ALLOC */
+
+void mutex_init_lockep(struct mutex *lock, const char *name, struct lock_class_key *key)
+{
+	__mutex_init_generic(lock);
+
+	/*
+	 * Make sure we are not reinitializing a held lock:
+	 */
+	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
+	lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_SLEEP);
+}
+EXPORT_SYMBOL(mutex_init_lockep);
+#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
 
 static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
 {

kernel/locking/mutex.h

@@ -59,15 +59,14 @@ extern void debug_mutex_add_waiter(struct mutex *lock,
 extern void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 				      struct task_struct *task);
 extern void debug_mutex_unlock(struct mutex *lock);
-extern void debug_mutex_init(struct mutex *lock, const char *name,
-			     struct lock_class_key *key);
+extern void debug_mutex_init(struct mutex *lock);
 #else /* CONFIG_DEBUG_MUTEXES */
 # define debug_mutex_lock_common(lock, waiter)		do { } while (0)
 # define debug_mutex_wake_waiter(lock, waiter)		do { } while (0)
 # define debug_mutex_free_waiter(waiter)		do { } while (0)
 # define debug_mutex_add_waiter(lock, waiter, ti)	do { } while (0)
 # define debug_mutex_remove_waiter(lock, waiter, ti)	do { } while (0)
 # define debug_mutex_unlock(lock)			do { } while (0)
-# define debug_mutex_init(lock, name, key)		do { } while (0)
+# define debug_mutex_init(lock)				do { } while (0)
 #endif /* !CONFIG_DEBUG_MUTEXES */
 #endif /* CONFIG_PREEMPT_RT */

kernel/locking/rtmutex_api.c

@@ -515,13 +515,11 @@ void rt_mutex_debug_task_free(struct task_struct *task)
 
 #ifdef CONFIG_PREEMPT_RT
 /* Mutexes */
-void __mutex_rt_init(struct mutex *mutex, const char *name,
-		     struct lock_class_key *key)
+static void __mutex_rt_init_generic(struct mutex *mutex)
 {
+	rt_mutex_base_init(&mutex->rtmutex);
 	debug_check_no_locks_freed((void *)mutex, sizeof(*mutex));
-	lockdep_init_map_wait(&mutex->dep_map, name, key, 0, LD_WAIT_SLEEP);
 }
-EXPORT_SYMBOL(__mutex_rt_init);
 
 static __always_inline int __mutex_lock_common(struct mutex *lock,
 					       unsigned int state,
@@ -542,6 +540,13 @@ static __always_inline int __mutex_lock_common(struct mutex *lock,
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
+void mutex_rt_init_lockdep(struct mutex *mutex, const char *name, struct lock_class_key *key)
+{
+	__mutex_rt_init_generic(mutex);
+	lockdep_init_map_wait(&mutex->dep_map, name, key, 0, LD_WAIT_SLEEP);
+}
+EXPORT_SYMBOL(mutex_rt_init_lockdep);
+
 void __sched mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 {
 	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
@@ -598,6 +603,12 @@ int __sched _mutex_trylock_nest_lock(struct mutex *lock,
 EXPORT_SYMBOL_GPL(_mutex_trylock_nest_lock);
 #else /* CONFIG_DEBUG_LOCK_ALLOC */
 
+void mutex_rt_init_generic(struct mutex *mutex)
+{
+	__mutex_rt_init_generic(mutex);
+}
+EXPORT_SYMBOL(mutex_rt_init_generic);
+
 void __sched mutex_lock(struct mutex *lock)
 {
 	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);