[PATCH RFC tip/core/rcu] Make rcu_irq_{enter,exit} check for NMI

[Paul E. McKenney]

Hello, Steve,

Yet another attempt to allow safe initiation of RCU voyeurism...

Untested at the moment.

                                                        Thanx, Paul

------------------------------------------------------------------------

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index db5eb8c3f7af..872d20cee00a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -891,6 +891,11 @@ void rcu_irq_exit(void)
 
        RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs 
enabled!!!");
        rdtp = this_cpu_ptr(&rcu_dynticks);
+
+       /* Page faults can happen in NMI handlers, so check... */
+       if (READ_ONCE(rdtp->dynticks_nmi_nesting))
+               return;
+
        WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
                     rdtp->dynticks_nesting < 1);
        if (rdtp->dynticks_nesting <= 1) {
@@ -1036,6 +1041,11 @@ void rcu_irq_enter(void)
 
        RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs 
enabled!!!");
        rdtp = this_cpu_ptr(&rcu_dynticks);
+
+       /* Page faults can happen in NMI handlers, so check... */
+       if (READ_ONCE(rdtp->dynticks_nmi_nesting))
+               return;
+
        oldval = rdtp->dynticks_nesting;
        rdtp->dynticks_nesting++;
        WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&