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>
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 2961ec7..4982998 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -109,6 +109,14 @@
}
#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 @@
*/
#define __irq_enter() \
do { \
+ rcu_irq_enter(); \
account_system_vtime(current); \
add_preempt_count(HARDIRQ_OFFSET); \
trace_hardirq_enter(); \
@@ -135,6 +144,7 @@
trace_hardirq_exit(); \
account_system_vtime(current); \
sub_preempt_count(HARDIRQ_OFFSET); \
+ rcu_irq_exit(); \
} while (0)
/*
diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index 4d66242..b3dccd6 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -160,5 +160,8 @@
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 */
diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
index 60c2a03..01152ed 100644
--- a/include/linux/rcupreempt.h
+++ b/include/linux/rcupreempt.h
@@ -82,5 +82,27 @@
struct softirq_action;
+#ifdef CONFIG_NO_HZ
+DECLARE_PER_CPU(long, dynticks_progress_counter);
+
+static inline void rcu_enter_nohz(void)
+{
+ __get_cpu_var(dynticks_progress_counter)++;
+ WARN_ON(__get_cpu_var(dynticks_progress_counter) & 0x1);
+ mb();
+}
+
+static inline void rcu_exit_nohz(void)
+{
+ mb();
+ __get_cpu_var(dynticks_progress_counter)++;
+ WARN_ON(!(__get_cpu_var(dynticks_progress_counter) & 0x1));
+}
+
+#else /* CONFIG_NO_HZ */
+#define rcu_enter_nohz() do { } while (0)
+#define rcu_exit_nohz() do { } while (0)
+#endif /* CONFIG_NO_HZ */
+
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUPREEMPT_H */