locking/spinlock: Provide RT variant

Provide the actual locking functions which make use of the general and
spinlock specific rtmutex code.
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/20210815211303.826621464@linutronix.de

kernel/locking/Makefile

@@ -25,6 +25,7 @@ obj-$(CONFIG_LOCK_SPIN_ON_OWNER) += osq_lock.o
 obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
 obj-$(CONFIG_QUEUED_SPINLOCKS) += qspinlock.o
 obj-$(CONFIG_RT_MUTEXES) += rtmutex_api.o
+obj-$(CONFIG_PREEMPT_RT) += spinlock_rt.o
 obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
 obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o
 obj-$(CONFIG_QUEUED_RWLOCKS) += qrwlock.o

kernel/locking/spinlock_rt.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * PREEMPT_RT substitution for spin/rw_locks
+ *
+ * spinlocks and rwlocks on RT are based on rtmutexes, with a few twists to
+ * resemble the non RT semantics:
+ *
+ * - Contrary to plain rtmutexes, spinlocks and rwlocks are state
+ *   preserving. The task state is saved before blocking on the underlying
+ *   rtmutex, and restored when the lock has been acquired. Regular wakeups
+ *   during that time are redirected to the saved state so no wake up is
+ *   missed.
+ *
+ * - Non RT spin/rwlocks disable preemption and eventually interrupts.
+ *   Disabling preemption has the side effect of disabling migration and
+ *   preventing RCU grace periods.
+ *
+ *   The RT substitutions explicitly disable migration and take
+ *   rcu_read_lock() across the lock held section.
+ */
+#include <linux/spinlock.h>
+#include <linux/export.h>
+
+#define RT_MUTEX_BUILD_SPINLOCKS
+#include "rtmutex.c"
+
+static __always_inline void rtlock_lock(struct rt_mutex_base *rtm)
+{
+	if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
+		rtlock_slowlock(rtm);
+}
+
+static __always_inline void __rt_spin_lock(spinlock_t *lock)
+{
+	___might_sleep(__FILE__, __LINE__, 0);
+	rtlock_lock(&lock->lock);
+	rcu_read_lock();
+	migrate_disable();
+}
+
+void __sched rt_spin_lock(spinlock_t *lock)
+{
+	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
+	__rt_spin_lock(lock);
+}
+EXPORT_SYMBOL(rt_spin_lock);
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+void __sched rt_spin_lock_nested(spinlock_t *lock, int subclass)
+{
+	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
+	__rt_spin_lock(lock);
+}
+EXPORT_SYMBOL(rt_spin_lock_nested);
+
+void __sched rt_spin_lock_nest_lock(spinlock_t *lock,
+				    struct lockdep_map *nest_lock)
+{
+	spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_);
+	__rt_spin_lock(lock);
+}
+EXPORT_SYMBOL(rt_spin_lock_nest_lock);
+#endif
+
+void __sched rt_spin_unlock(spinlock_t *lock)
+{
+	spin_release(&lock->dep_map, _RET_IP_);
+	migrate_enable();
+	rcu_read_unlock();
+
+	if (unlikely(!rt_mutex_cmpxchg_release(&lock->lock, current, NULL)))
+		rt_mutex_slowunlock(&lock->lock);
+}
+EXPORT_SYMBOL(rt_spin_unlock);
+
+/*
+ * Wait for the lock to get unlocked: instead of polling for an unlock
+ * (like raw spinlocks do), lock and unlock, to force the kernel to
+ * schedule if there's contention:
+ */
+void __sched rt_spin_lock_unlock(spinlock_t *lock)
+{
+	spin_lock(lock);
+	spin_unlock(lock);
+}
+EXPORT_SYMBOL(rt_spin_lock_unlock);
+
+static __always_inline int __rt_spin_trylock(spinlock_t *lock)
+{
+	int ret = 1;
+
+	if (unlikely(!rt_mutex_cmpxchg_acquire(&lock->lock, NULL, current)))
+		ret = rt_mutex_slowtrylock(&lock->lock);
+
+	if (ret) {
+		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
+		rcu_read_lock();
+		migrate_disable();
+	}
+	return ret;
+}
+
+int __sched rt_spin_trylock(spinlock_t *lock)
+{
+	return __rt_spin_trylock(lock);
+}
+EXPORT_SYMBOL(rt_spin_trylock);
+
+int __sched rt_spin_trylock_bh(spinlock_t *lock)
+{
+	int ret;
+
+	local_bh_disable();
+	ret = __rt_spin_trylock(lock);
+	if (!ret)
+		local_bh_enable();
+	return ret;
+}
+EXPORT_SYMBOL(rt_spin_trylock_bh);
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+void __rt_spin_lock_init(spinlock_t *lock, const char *name,
+			 struct lock_class_key *key)
+{
+	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
+	lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_CONFIG);
+}
+EXPORT_SYMBOL(__rt_spin_lock_init);
+#endif