Subject: [PATCH v3 1/1] rust: helpers: Avoid raw_spin_lock initialization for PREEMPT_RT

From: Eder Zulian <[email-masked]>
Date: Thu, 7 Nov 2024 17:32:23 +0100

When PREEMPT_RT=y, spin locks are mapped to rt_mutex types, so using
spinlock_check() + __raw_spin_lock_init() to initialize spin locks is
incorrect, and would cause build errors.

Introduce __spin_lock_init() to initialize a spin lock with lockdep
rquired information for PREEMPT_RT builds, and use it in the Rust
helper.

Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.")
Reported-by: kernel test robot <[email-masked]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email-masked]/
Signed-off-by: Eder Zulian <[email-masked]>
---
V1 -> V2: Cleaned up style and addressed review comments
V2 -> V3: Improved commit title and description and corrected the 'Fixed:'
tag as per reviewer's suggestion

 include/linux/spinlock_rt.h | 15 +++++++--------
 rust/helpers/spinlock.c     |  8 ++++++--
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/include/linux/spinlock_rt.h b/include/linux/spinlock_rt.h
index f9f14e135be7..f6499c37157d 100644
--- a/include/linux/spinlock_rt.h
+++ b/include/linux/spinlock_rt.h
@@ -16,22 +16,21 @@ static inline void __rt_spin_lock_init(spinlock_t *lock, const char *name,
 }
 #endif
 
-#define spin_lock_init(slock)					\
+#define __spin_lock_init(slock, name, key, percpu)		\
 do {								\
-	static struct lock_class_key __key;			\
-								\
 	rt_mutex_base_init(&(slock)->lock);			\
-	__rt_spin_lock_init(slock, #slock, &__key, false);	\
+	__rt_spin_lock_init(slock, name, key, percpu);		\
 } while (0)
 
-#define local_spin_lock_init(slock)				\
+#define _spin_lock_init(slock, percpu)				\
 do {								\
 	static struct lock_class_key __key;			\
-								\
-	rt_mutex_base_init(&(slock)->lock);			\
-	__rt_spin_lock_init(slock, #slock, &__key, true);	\
+	__spin_lock_init(slock, #slock, &__key, percpu);	\
 } while (0)
 
+#define spin_lock_init(slock)		_spin_lock_init(slock, false)
+#define local_spin_lock_init(slock)	_spin_lock_init(slock, true)
+
 extern void rt_spin_lock(spinlock_t *lock) __acquires(lock);
 extern void rt_spin_lock_nested(spinlock_t *lock, int subclass)	__acquires(lock);
 extern void rt_spin_lock_nest_lock(spinlock_t *lock, struct lockdep_map *nest_lock) __acquires(lock);
diff --git a/rust/helpers/spinlock.c b/rust/helpers/spinlock.c
index b7b0945e8b3c..5971fdf6f755 100644
--- a/rust/helpers/spinlock.c
+++ b/rust/helpers/spinlock.c
@@ -6,10 +6,14 @@ void rust_helper___spin_lock_init(spinlock_t *lock, const char *name,
 				  struct lock_class_key *key)
 {
 #ifdef CONFIG_DEBUG_SPINLOCK
+# if defined(CONFIG_PREEMPT_RT)
+	__spin_lock_init(lock, name, key, false);
+# else /*!CONFIG_PREEMPT_RT */
 	__raw_spin_lock_init(spinlock_check(lock), name, key, LD_WAIT_CONFIG);
-#else
+# endif /* CONFIG_PREEMPT_RT */
+#else /* !CONFIG_DEBUG_SPINLOCK */
 	spin_lock_init(lock);
-#endif
+#endif /* CONFIG_DEBUG_SPINLOCK */
 }
 
 void rust_helper_spin_lock(spinlock_t *lock)
-- 
2.47.0