rcu: add support for dynamic ticks and preempt rcu

The PREEMPT-RCU can get stuck if a CPU goes idle and NO_HZ is set. The
idle CPU will not progress the RCU through its grace period and a
synchronize_rcu my get stuck. Without this patch I have a box that will
not boot when PREEMPT_RCU and NO_HZ are set. That same box boots fine
with this patch.

This patch comes from the -rt kernel where it has been tested for
several months.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index 4d6624260b4c..b3dccd68629e 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -160,5 +160,8 @@ extern void rcu_restart_cpu(int cpu);
 extern long rcu_batches_completed(void);
 extern long rcu_batches_completed_bh(void);
 
+#define rcu_enter_nohz()        do { } while (0)
+#define rcu_exit_nohz()         do { } while (0)
+
 #endif /* __KERNEL__ */
 #endif /* __LINUX_RCUCLASSIC_H */