[patch V9 03/39] rcu: Provide rcu_irq_exit_check_preempt()

[Thomas Gleixner]

Provide a debug check which can be invoked from exception return to kernel
mode before an attempt is made to schedule. Warn if RCU is not ready for
this.

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
V9: New patch
---
 include/linux/rcutiny.h |    1 +
 include/linux/rcutree.h |    6 ++++++
 kernel/rcu/tree.c       |   18 ++++++++++++++++++
 3 files changed, 25 insertions(+)

--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -72,6 +72,7 @@ static inline void rcu_irq_exit_irqson(v
 static inline void rcu_irq_enter_irqson(void) { }
 static inline void rcu_irq_exit(void) { }
 static inline void rcu_irq_exit_preempt(void) { }
+static inline void rcu_irq_exit_check_preempt(void) { }
 static inline void exit_rcu(void) { }
 static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 {
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -51,6 +51,12 @@ void rcu_irq_exit_preempt(void);
 void rcu_irq_enter_irqson(void);
 void rcu_irq_exit_irqson(void);
 
+#ifdef CONFIG_PROVE_RCU
+void rcu_irq_exit_check_preempt(void);
+#else
+static inline void rcu_irq_exit_check_preempt(void) { }
+#endif
+
 void exit_rcu(void);
 
 void rcu_scheduler_starting(void);
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -765,6 +765,24 @@ void rcu_irq_exit_preempt(void)
                         "RCU in extended quiescent state!");
 }
 
+#ifdef CONFIG_PROVE_RCU
+/**
+ * rcu_irq_exit_check_preempt - Validate that scheduling is possible
+ */
+void rcu_irq_exit_check_preempt(void)
+{
+       lockdep_assert_irqs_disabled();
+
+       RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) <= 0,
+                        "RCU dynticks_nesting counter underflow/zero!");
+       RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) !=
+                        DYNTICK_IRQ_NONIDLE,
+                        "Bad RCU  dynticks_nmi_nesting counter\n");
+       RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
+                        "RCU in extended quiescent state!");
+}
+#endif /* #ifdef CONFIG_PROVE_RCU */
+
 /*
  * Wrapper for rcu_irq_exit() where interrupts are enabled.
  *