locking/spinlock: Provide RT specific spinlock_t

RT replaces spinlocks with a simple wrapper around an rtmutex, which turns
spinlocks on RT into 'sleeping' spinlocks. The actual implementation of the
spinlock API differs from a regular rtmutex, as it does neither handle
timeouts nor signals and it is state preserving across the lock operation.

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/20210815211303.654230709@linutronix.de

include/linux/spinlock_types.h

@@ -11,6 +11,9 @@
 
 #include <linux/spinlock_types_raw.h>
 
+#ifndef CONFIG_PREEMPT_RT
+
+/* Non PREEMPT_RT kernels map spinlock to raw_spinlock */
 typedef struct spinlock {
 	union {
 		struct raw_spinlock rlock;
@@ -39,6 +42,29 @@ typedef struct spinlock {
 
 #define DEFINE_SPINLOCK(x)	spinlock_t x = __SPIN_LOCK_UNLOCKED(x)
 
+#else /* !CONFIG_PREEMPT_RT */
+
+/* PREEMPT_RT kernels map spinlock to rt_mutex */
+#include <linux/rtmutex.h>
+
+typedef struct spinlock {
+	struct rt_mutex_base	lock;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map	dep_map;
+#endif
+} spinlock_t;
+
+#define __SPIN_LOCK_UNLOCKED(name)				\
+	{							\
+		.lock = __RT_MUTEX_BASE_INITIALIZER(name.lock),	\
+		SPIN_DEP_MAP_INIT(name)				\
+	}
+
+#define DEFINE_SPINLOCK(name)					\
+	spinlock_t name = __SPIN_LOCK_UNLOCKED(name)
+
+#endif /* CONFIG_PREEMPT_RT */
+
 #include <linux/rwlock_types.h>
 
 #endif /* __LINUX_SPINLOCK_TYPES_H */