[tip: x86/entry] rcu: Provide rcu_irq_exit_check_preempt()

["tip-bot2 for Thomas Gleixner" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     07325d4a90d2d84de45cc07b134fd0f023dbb971
Gitweb:        https://git.kernel.org/tip/07325d4a90d2d84de45cc07b134fd0f023dbb971
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Thu, 21 May 2020 22:05:16 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 26 May 2020 19:05:11 +02:00

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
---
 include/linux/rcutiny.h |  1 +
 include/linux/rcutree.h |  6 ++++++
 kernel/rcu/tree.c       | 18 ++++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index c869fb2..8512cae 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 9366fa4..d5cc9d6 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 b7f8c49..d8e9dbb 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.
  *