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

From: Paul E. McKenney
Date: Fri Sep 22 2017 - 16:14:08 EST


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) &&