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, 10 insertions, 0 deletions

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 2961ec788046..49829988bfa0 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -109,6 +109,14 @@ static inline void account_system_vtime(struct task_struct *tsk)
 }
 #endif
 
+#if defined(CONFIG_PREEMPT_RCU) && defined(CONFIG_NO_HZ)
+extern void rcu_irq_enter(void);
+extern void rcu_irq_exit(void);
+#else
+# define rcu_irq_enter() do { } while (0)
+# define rcu_irq_exit() do { } while (0)
+#endif /* CONFIG_PREEMPT_RCU */
+
 /*
  * It is safe to do non-atomic ops on ->hardirq_context,
  * because NMI handlers may not preempt and the ops are
@@ -117,6 +125,7 @@ static inline void account_system_vtime(struct task_struct *tsk)
  */
 #define __irq_enter()                                   \
         do {                                            \
+                rcu_irq_enter();                        \
                 account_system_vtime(current);          \
                 add_preempt_count(HARDIRQ_OFFSET);      \
                 trace_hardirq_enter();                  \
@@ -135,6 +144,7 @@ extern void irq_enter(void);
                 trace_hardirq_exit();                   \
                 account_system_vtime(current);          \
                 sub_preempt_count(HARDIRQ_OFFSET);      \
+                rcu_irq_exit();                         \
         } while (0)
 
 /*