stomp-machine: create lg_global_trylock_relax() primitive

Create lg_global_trylock_relax() for use by stopper thread when it cannot
schedule, to deal with stop_cpus_lock, which is now an lglock.

Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

include/linux/lglock.h

@@ -74,4 +74,10 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu);
 void lg_global_lock(struct lglock *lg);
 void lg_global_unlock(struct lglock *lg);
 
+#ifndef CONFIG_PREEMPT_RT_FULL
+#define lg_global_trylock_relax(name)	lg_global_lock(name)
+#else
+void lg_global_trylock_relax(struct lglock *lg);
+#endif
+
 #endif

include/linux/spinlock_rt.h

@@ -35,6 +35,7 @@ extern int atomic_dec_and_spin_lock(atomic_t *atomic, spinlock_t *lock);
  */
 extern void __lockfunc __rt_spin_lock(struct rt_mutex *lock);
 extern void __lockfunc __rt_spin_unlock(struct rt_mutex *lock);
+extern int __lockfunc __rt_spin_trylock(struct rt_mutex *lock);
 
 #define spin_lock(lock)				\
 	do {					\

kernel/locking/lglock.c

@@ -105,3 +105,28 @@ void lg_global_unlock(struct lglock *lg)
 	preempt_enable_nort();
 }
 EXPORT_SYMBOL(lg_global_unlock);
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+/*
+ * HACK: If you use this, you get to keep the pieces.
+ * Used in queue_stop_cpus_work() when stop machinery
+ * is called from inactive CPU, so we can't schedule.
+ */
+# define lg_do_trylock_relax(l)			\
+	do {					\
+		while (!__rt_spin_trylock(l))	\
+			cpu_relax();		\
+	} while (0)
+
+void lg_global_trylock_relax(struct lglock *lg)
+{
+	int i;
+
+	lock_acquire_exclusive(&lg->lock_dep_map, 0, 0, NULL, _RET_IP_);
+	for_each_possible_cpu(i) {
+		lg_lock_ptr *lock;
+		lock = per_cpu_ptr(lg->lock, i);
+		lg_do_trylock_relax(lock);
+	}
+}
+#endif

kernel/locking/rtmutex.c

@@ -1139,6 +1139,11 @@ void __lockfunc rt_spin_unlock_wait(spinlock_t *lock)
 }
 EXPORT_SYMBOL(rt_spin_unlock_wait);
 
+int __lockfunc __rt_spin_trylock(struct rt_mutex *lock)
+{
+	return rt_mutex_trylock(lock);
+}
+
 int __lockfunc rt_spin_trylock(spinlock_t *lock)
 {
 	int ret = rt_mutex_trylock(&lock->lock);