From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 21 May 2020 20:05:16 +0000 (+0200)
Subject: rcu: Provide rcu_irq_exit_check_preempt()
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=07325d4a90d2d84de45cc07b134fd0f023dbb971;p=linux.git

rcu: Provide rcu_irq_exit_check_preempt()

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 <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20200521202117.089709607@linutronix.de
---

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index c869fb20cc510..8512caeb76822 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -72,6 +72,7 @@ static inline void rcu_irq_exit_irqson(void) { }
 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)
 {
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 9366fa4d0717b..d5cc9d6759879 100644
--- 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);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b7f8c494d1d16..d8e9dbbefcfae 100644
--- 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.
  *