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
  | 30233269  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   36412269  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

1 files changed, 22 insertions, 6 deletions

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index de7d6702cd96..2a1d165b3167 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -43,8 +43,7 @@
 # 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);
@@ -52,10 +51,8 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 #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)
 {