ENGR00156637 [MX6]Reboot take long time on SMP

Add work around to the reboot issue of SMP, with
SMP, all the CPUs need to do _rcu_barrier, if we
enqueue an rcu callback, we need to make sure CPU
tick to stay alive until we take care of those by
completing the appropriate grace period.

This work around only work when the reboot command
issue, so it didn't impact normal kernel feature.

Signed-off-by: Anson Huang <b20788@freescale.com>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ba06207b1dd3bf9f9d42bc8800998b80b909c02d..3585b42eb7cbbcd38f463ff69d8d63263e1ef593 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -50,6 +50,7 @@
 #include <linux/wait.h>
 #include <linux/kthread.h>
 #include <linux/prefetch.h>
+#include <linux/tick.h>
 
 #include "rcutree.h"
 
@@ -1480,6 +1481,7 @@ static void rcu_process_callbacks(struct softirq_action *unused)
        /* If we are last CPU on way to dyntick-idle mode, accelerate it. */
        rcu_needs_cpu_flush();
 }
+static atomic_t rcu_barrier_cpu_count;
 
 /*
  * Wake up the current CPU's kthread.  This replaces raise_softirq()
@@ -1536,6 +1538,14 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
                return;
        }
 
+       /* Work around for reboot issue, check rcu_barrier_cpu_count
+       to see whether it is in the _rcu_barrier process, do
+       tick_nohz_restart_sched_tick if yes. If we enqueue an rcu
+       callback, we need the CPU tick to stay alive until we take care
+       of those by completing the appropriate grace period. */
+       if (atomic_read(&rcu_barrier_cpu_count) != 0)
+               tick_nohz_restart_sched_tick();
+
        /*
         * Force the grace period if too many callbacks or too long waiting.
         * Enforce hysteresis, and don't invoke force_quiescent_state()
@@ -1750,7 +1760,6 @@ static int rcu_needs_cpu_quick_check(int cpu)
 }
 
 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
-static atomic_t rcu_barrier_cpu_count;
 static DEFINE_MUTEX(rcu_barrier_mutex);
 static struct completion rcu_barrier_completion;