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Message-ID: <20251123010157.2076095-1-longman@redhat.com>
Date: Sat, 22 Nov 2025 20:01:57 -0500
From: Waiman Long <longman@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Will Deacon <will@...nel.org>,
Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Waiman Long <longman@...hat.com>
Subject: [PATCH] locking/rwsem: Redo __rwsem_init()
This is a rwsem version of the Sebastian's commit 3572e2edc7b6
("locking/mutex: Redo __mutex_init()"). The aim is to avoid storing
the lock name strings which consume memory that are never used.
The __rwsem_init() will be split into a _generic version with lockdep
(CONFIG_DEBUG_LOCK_ALLOC) disabled and a _lockdep version when it
is enabled. This will make the rwsem code behavior similar to the
mutex code.
This results in the following kernel size reduction with defconfig
based config files:
text data bss dec filename
30200741 8165526 1188464 39554731 vmlinux
30200725 8161430 1188464 39550619 vmlinux (patched)
32417939 8475218 12946524 53839681 vmlinux.lockdep
32417945 8475218 12946524 53839687 vmlinux.lockdep (patched)
27119989 7195918 2075852 36391759 vmlinux.preempt_rt
27119996 7195918 2075852 36391766 vmlinux.preempt_rt (patched)
29349572 7509862 13792416 50651850 vmlinux.preempt_rt.lockdep
The kernel size reduction for the lockdep disabled cases isn't that
noticeable when compared with the mutex case as there is an order
of magnitude more mutex_init() calls than the init_rwsem() calls in
the kernel.
Signed-off-by: Waiman Long <longman@...hat.com>
---
include/linux/rwsem.h | 45 +++++++++++++++++++++++++++++++++------
kernel/locking/rwsem.c | 48 ++++++++++++++++++++++++++++--------------
2 files changed, 71 insertions(+), 22 deletions(-)
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index f1aaf676a874..4045ddf2b698 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -111,15 +111,32 @@ static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *
#define DECLARE_RWSEM(name) \
struct rw_semaphore name = __RWSEM_INITIALIZER(name)
-extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
- struct lock_class_key *key);
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+extern void rwsem_init_generic(struct rw_semaphore *sem);
+
+static inline void __init_rwsem(struct rw_semaphore *sem, const char *name,
+ struct lock_class_key *key)
+{
+ rwsem_init_generic(sem);
+}
+
+#define init_rwsem(sem) rwsem_init_generic(sem)
+#else
+extern void rwsem_init_lockdep(struct rw_semaphore *sem, const char *name,
+ struct lock_class_key *key);
+static inline void __init_rwsem(struct rw_semaphore *sem, const char *name,
+ struct lock_class_key *key)
+{
+ rwsem_init_lockdep(sem, name, key);
+}
#define init_rwsem(sem) \
do { \
static struct lock_class_key __key; \
\
- __init_rwsem((sem), #sem, &__key); \
+ rwsem_init_lockdep((sem), #sem, &__key); \
} while (0)
+#endif /* CONFIG_DEBUG_LOCK_ALLOC */
/*
* This is the same regardless of which rwsem implementation that is being used.
@@ -164,15 +181,31 @@ struct rw_semaphore {
#define DECLARE_RWSEM(lockname) \
struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname)
-extern void __init_rwsem(struct rw_semaphore *rwsem, const char *name,
- struct lock_class_key *key);
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+extern void rwsem_rt_init_generic(struct rw_semaphore *rwsem);
+static inline void __init_rwsem(struct rw_semaphore *rwsem, const char *name,
+ struct lock_class_key *key)
+{
+ rwsem_rt_init_generic(rwsem);
+}
+
+#define init_rwsem(sem) rwsem_rt_init_generic(sem)
+#else
+extern void rwsem_rt_init_lockdep(struct rw_semaphore *rwsem, const char *name,
+ struct lock_class_key *key);
+static inline void __init_rwsem(struct rw_semaphore *rwsem, const char *name,
+ struct lock_class_key *key)
+{
+ rwsem_rt_init_lockdep(rwsem, name, key);
+}
#define init_rwsem(sem) \
do { \
static struct lock_class_key __key; \
\
- __init_rwsem((sem), #sem, &__key); \
+ rwsem_rt_init_lockdep((sem), #sem, &__key); \
} while (0)
+#endif /* CONFIG_DEBUG_LOCK_ALLOC */
static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem)
{
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 24df4d98f7d2..ffb09e0520c9 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -306,16 +306,8 @@ rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
/*
* Initialize an rwsem:
*/
-void __init_rwsem(struct rw_semaphore *sem, const char *name,
- struct lock_class_key *key)
+static inline void __rwsem_init_generic(struct rw_semaphore *sem)
{
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
- /*
- * Make sure we are not reinitializing a held semaphore:
- */
- debug_check_no_locks_freed((void *)sem, sizeof(*sem));
- lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
-#endif
#ifdef CONFIG_DEBUG_RWSEMS
sem->magic = sem;
#endif
@@ -327,7 +319,26 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
osq_lock_init(&sem->osq);
#endif
}
-EXPORT_SYMBOL(__init_rwsem);
+
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+void rwsem_init_generic(struct rw_semaphore *sem)
+{
+ __rwsem_init_generic(sem);
+}
+EXPORT_SYMBOL(rwsem_init_generic);
+#else
+void rwsem_init_lockdep(struct rw_semaphore *sem, const char *name,
+ struct lock_class_key *key)
+{
+ /*
+ * Make sure we are not reinitializing a held semaphore:
+ */
+ debug_check_no_locks_freed((void *)sem, sizeof(*sem));
+ lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
+ __rwsem_init_generic(sem);
+}
+EXPORT_SYMBOL(rwsem_init_lockdep);
+#endif /* CONFIG_DEBUG_LOCK_ALLOC */
enum rwsem_waiter_type {
RWSEM_WAITING_FOR_WRITE,
@@ -1449,17 +1460,22 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
#include "rwbase_rt.c"
-void __init_rwsem(struct rw_semaphore *sem, const char *name,
- struct lock_class_key *key)
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+void rwsem_rt_init_generic(struct rw_semaphore *sem)
+{
+ init_rwbase_rt(&(sem)->rwbase);
+}
+EXPORT_SYMBOL(rwsem_rt_init_generic);
+#else
+void rwsem_rt_init_lockdep(struct rw_semaphore *sem, const char *name,
+ struct lock_class_key *key)
{
init_rwbase_rt(&(sem)->rwbase);
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
-#endif
}
-EXPORT_SYMBOL(__init_rwsem);
+EXPORT_SYMBOL(rwsem_rt_init_lockdep);
+#endif /* CONFIG_DEBUG_LOCK_ALLOC */
static inline void __down_read(struct rw_semaphore *sem)
{
--
2.51.1
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