locking/spinlock: Provide RT variant header: <linux/spinlock_rt.h>

Provide the necessary wrappers around the actual rtmutex based spinlock
implementation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.712897671@linutronix.de

include/linux/spinlock.h

@@ -312,8 +312,10 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 	1 : ({ local_irq_restore(flags); 0; }); \
 })
 
-/* Include rwlock functions */
+#ifndef CONFIG_PREEMPT_RT
+/* Include rwlock functions for !RT */
 #include <linux/rwlock.h>
+#endif
 
 /*
  * Pull the _spin_*()/_read_*()/_write_*() functions/declarations:
@@ -324,6 +326,9 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 # include <linux/spinlock_api_up.h>
 #endif
 
+/* Non PREEMPT_RT kernel, map to raw spinlocks: */
+#ifndef CONFIG_PREEMPT_RT
+
 /*
  * Map the spin_lock functions to the raw variants for PREEMPT_RT=n
  */
@@ -458,6 +463,10 @@ static __always_inline int spin_is_contended(spinlock_t *lock)
 
 #define assert_spin_locked(lock)	assert_raw_spin_locked(&(lock)->rlock)
 
+#else  /* !CONFIG_PREEMPT_RT */
+# include <linux/spinlock_rt.h>
+#endif /* CONFIG_PREEMPT_RT */
+
 /*
  * Pull the atomic_t declaration:
  * (asm-mips/atomic.h needs above definitions)

include/linux/spinlock_api_smp.h

@@ -187,6 +187,9 @@ static inline int __raw_spin_trylock_bh(raw_spinlock_t *lock)
 	return 0;
 }
 
+/* PREEMPT_RT has its own rwlock implementation */
+#ifndef CONFIG_PREEMPT_RT
 #include <linux/rwlock_api_smp.h>
+#endif
 
 #endif /* __LINUX_SPINLOCK_API_SMP_H */

include/linux/spinlock_rt.h

+// SPDX-License-Identifier: GPL-2.0-only
+#ifndef __LINUX_SPINLOCK_RT_H
+#define __LINUX_SPINLOCK_RT_H
+
+#ifndef __LINUX_SPINLOCK_H
+#error Do not include directly. Use spinlock.h
+#endif
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern void __rt_spin_lock_init(spinlock_t *lock, const char *name,
+				struct lock_class_key *key);
+#else
+static inline void __rt_spin_lock_init(spinlock_t *lock, const char *name,
+				       struct lock_class_key *key)
+{
+}
+#endif
+
+#define spin_lock_init(slock)				\
+do {							\
+	static struct lock_class_key __key;		\
+							\
+	rt_mutex_base_init(&(slock)->lock);		\
+	__rt_spin_lock_init(slock, #slock, &__key);	\
+} while (0)
+
+extern void rt_spin_lock(spinlock_t *lock);
+extern void rt_spin_lock_nested(spinlock_t *lock, int subclass);
+extern void rt_spin_lock_nest_lock(spinlock_t *lock, struct lockdep_map *nest_lock);
+extern void rt_spin_unlock(spinlock_t *lock);
+extern void rt_spin_lock_unlock(spinlock_t *lock);
+extern int rt_spin_trylock_bh(spinlock_t *lock);
+extern int rt_spin_trylock(spinlock_t *lock);
+
+static __always_inline void spin_lock(spinlock_t *lock)
+{
+	rt_spin_lock(lock);
+}
+
+#ifdef CONFIG_LOCKDEP
+# define __spin_lock_nested(lock, subclass)				\
+	rt_spin_lock_nested(lock, subclass)
+
+# define __spin_lock_nest_lock(lock, nest_lock)				\
+	do {								\
+		typecheck(struct lockdep_map *, &(nest_lock)->dep_map);	\
+		rt_spin_lock_nest_lock(lock, &(nest_lock)->dep_map);	\
+	} while (0)
+# define __spin_lock_irqsave_nested(lock, flags, subclass)	\
+	do {							\
+		typecheck(unsigned long, flags);		\
+		flags = 0;					\
+		__spin_lock_nested(lock, subclass);		\
+	} while (0)
+
+#else
+ /*
+  * Always evaluate the 'subclass' argument to avoid that the compiler
+  * warns about set-but-not-used variables when building with
+  * CONFIG_DEBUG_LOCK_ALLOC=n and with W=1.
+  */
+# define __spin_lock_nested(lock, subclass)	spin_lock(((void)(subclass), (lock)))
+# define __spin_lock_nest_lock(lock, subclass)	spin_lock(((void)(subclass), (lock)))
+# define __spin_lock_irqsave_nested(lock, flags, subclass)	\
+	spin_lock_irqsave(((void)(subclass), (lock)), flags)
+#endif
+
+#define spin_lock_nested(lock, subclass)		\
+	__spin_lock_nested(lock, subclass)
+
+#define spin_lock_nest_lock(lock, nest_lock)		\
+	__spin_lock_nest_lock(lock, nest_lock)
+
+#define spin_lock_irqsave_nested(lock, flags, subclass)	\
+	__spin_lock_irqsave_nested(lock, flags, subclass)
+
+static __always_inline void spin_lock_bh(spinlock_t *lock)
+{
+	/* Investigate: Drop bh when blocking ? */
+	local_bh_disable();
+	rt_spin_lock(lock);
+}
+
+static __always_inline void spin_lock_irq(spinlock_t *lock)
+{
+	rt_spin_lock(lock);
+}
+
+#define spin_lock_irqsave(lock, flags)			 \
+	do {						 \
+		typecheck(unsigned long, flags);	 \
+		flags = 0;				 \
+		spin_lock(lock);			 \
+	} while (0)
+
+static __always_inline void spin_unlock(spinlock_t *lock)
+{
+	rt_spin_unlock(lock);
+}
+
+static __always_inline void spin_unlock_bh(spinlock_t *lock)
+{
+	rt_spin_unlock(lock);
+	local_bh_enable();
+}
+
+static __always_inline void spin_unlock_irq(spinlock_t *lock)
+{
+	rt_spin_unlock(lock);
+}
+
+static __always_inline void spin_unlock_irqrestore(spinlock_t *lock,
+						   unsigned long flags)
+{
+	rt_spin_unlock(lock);
+}
+
+#define spin_trylock(lock)				\
+	__cond_lock(lock, rt_spin_trylock(lock))
+
+#define spin_trylock_bh(lock)				\
+	__cond_lock(lock, rt_spin_trylock_bh(lock))
+
+#define spin_trylock_irq(lock)				\
+	__cond_lock(lock, rt_spin_trylock(lock))
+
+#define __spin_trylock_irqsave(lock, flags)		\
+({							\
+	int __locked;					\
+							\
+	typecheck(unsigned long, flags);		\
+	flags = 0;					\
+	__locked = spin_trylock(lock);			\
+	__locked;					\
+})
+
+#define spin_trylock_irqsave(lock, flags)		\
+	__cond_lock(lock, __spin_trylock_irqsave(lock, flags))
+
+#define spin_is_contended(lock)		(((void)(lock), 0))
+
+static inline int spin_is_locked(spinlock_t *lock)
+{
+	return rt_mutex_base_is_locked(&lock->lock);
+}
+
+#define assert_spin_locked(lock) BUG_ON(!spin_is_locked(lock))
+
+#endif