RCU: skip the "schedule() in RCU section" warning on UP, too

In "RCU: we need to skip that warning but only on sleeping locks" we
skipped a warning on SMP systems in case we schedule out in a RCU
section while attempt to obtain a sleeping lock. This is also required
on UP systems.
In order to do so, I introduce a tiny version of migrate_disable() +
_enable() which only update the counters which we then can check against
on RT && !SMP.

Cc: [email protected]
Reported-by: Grygorii Strashko <[email protected]>
Tested-by: Grygorii Strashko <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>

Author: Sebastian Andrzej Siewior

include/linux/preempt.h

@@ -211,6 +211,15 @@ extern void migrate_enable(void);
 
 int __migrate_disabled(struct task_struct *p);
 
+#elif !defined(CONFIG_SMP) && defined(CONFIG_PREEMPT_RT_BASE)
+
+extern void migrate_disable(void);
+extern void migrate_enable(void);
+static inline int __migrate_disabled(struct task_struct *p)
+{
+	return 0;
+}
+
 #else
 #define migrate_disable()		barrier()
 #define migrate_enable()		barrier()

include/linux/sched.h

@@ -591,6 +591,12 @@ struct task_struct {
 # ifdef CONFIG_SCHED_DEBUG
 	int				migrate_disable_atomic;
 # endif
+
+#elif !defined(CONFIG_SMP) && defined(CONFIG_PREEMPT_RT_BASE)
+	int				migrate_disable;
+# ifdef CONFIG_SCHED_DEBUG
+	int				migrate_disable_atomic;
+# endif
 #endif
 
 #ifdef CONFIG_PREEMPT_RCU

kernel/rcu/tree_plugin.h

@@ -326,7 +326,7 @@ static void rcu_preempt_note_context_switch(bool preempt)
 	int mg_counter = 0;
 
 	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_preempt_note_context_switch() invoked with interrupts enabled!!!\n");
-#if defined(CONFIG_PREEMPT_COUNT) && defined(CONFIG_SMP)
+#if defined(CONFIG_PREEMPT_RT_BASE)
 	mg_counter = t->migrate_disable;
 #endif
 	WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !mg_counter);

kernel/sched/core.c

@@ -7020,4 +7020,49 @@ void migrate_enable(void)
 	preempt_enable();
 }
 EXPORT_SYMBOL(migrate_enable);
+
+#elif !defined(CONFIG_SMP) && defined(CONFIG_PREEMPT_RT_BASE)
+void migrate_disable(void)
+{
+	struct task_struct *p = current;
+
+	if (in_atomic() || irqs_disabled()) {
+#ifdef CONFIG_SCHED_DEBUG
+		p->migrate_disable_atomic++;
+#endif
+		return;
+	}
+#ifdef CONFIG_SCHED_DEBUG
+	if (unlikely(p->migrate_disable_atomic)) {
+		tracing_off();
+		WARN_ON_ONCE(1);
+	}
+#endif
+
+	p->migrate_disable++;
+}
+EXPORT_SYMBOL(migrate_disable);
+
+void migrate_enable(void)
+{
+	struct task_struct *p = current;
+
+	if (in_atomic() || irqs_disabled()) {
+#ifdef CONFIG_SCHED_DEBUG
+		p->migrate_disable_atomic--;
+#endif
+		return;
+	}
+
+#ifdef CONFIG_SCHED_DEBUG
+	if (unlikely(p->migrate_disable_atomic)) {
+		tracing_off();
+		WARN_ON_ONCE(1);
+	}
+#endif
+
+	WARN_ON_ONCE(p->migrate_disable <= 0);
+	p->migrate_disable--;
+}
+EXPORT_SYMBOL(migrate_enable);
 #endif