[PATCH] sched: idle: move need_resched check after function rcu_idle_enter

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From	Lianwei Wang <lianwei.wang@gmail.com>
Newsgroups	linux.kernel
Subject	[PATCH] sched: idle: move need_resched check after function rcu_idle_enter
Date	Sat, 21 Nov 2015 10:10:01 +0100
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The rcu_idle_endter may call wakeup_softirqd to set the need resched
flag on idle process. But if we don't check it after that, then the
cpu will enter idle state with RESCHED flag set and can not be woken
up by wakeup/resched call anymore.

Check need_resched after rcu_idle_enter to make sure the cpu is able
to be out of idle immediatley to run other tasks.

Signed-off-by: Lianwei Wang <lianwei.wang@gmail.com>
---
 kernel/sched/idle.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 4a2ef5a02fd3..6e96a1f41041 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -137,21 +137,21 @@ static void cpuidle_idle_call(void)
        int next_state, entered_state;

        /*
+        * Tell the RCU framework we are entering an idle section,
+        * so no more rcu read side critical sections and one more
+        * step to the grace period
+        */
+       rcu_idle_enter();
+
+       /*
         * Check if the idle task must be rescheduled. If it is the
         * case, exit the function after re-enabling the local irq.
         */
        if (need_resched()) {
                local_irq_enable();
-               return;
+               goto exit_idle;
        }

-       /*
-        * Tell the RCU framework we are entering an idle section,
-        * so no more rcu read side critical sections and one more
-        * step to the grace period
-        */
-       rcu_idle_enter();
-
        if (cpuidle_not_available(drv, dev)) {
                default_idle_call();
                goto exit_idle;
--
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[PATCH] sched: idle: move need_resched check after function rcu_idle_enter Lianwei Wang <lianwei.wang@gmail.com> - 2015-11-21 10:10 +0100
  Re: [PATCH] sched: idle: move need_resched check after function  rcu_idle_enter Peter Zijlstra <peterz@infradead.org> - 2015-11-23 14:10 +0100
    Re: [PATCH] sched: idle: move need_resched check after function rcu_idle_enter Lianwei Wang <lianwei.wang@gmail.com> - 2015-11-23 18:50 +0100
      Re: [PATCH] sched: idle: move need_resched check after function  rcu_idle_enter Peter Zijlstra <peterz@infradead.org> - 2015-11-23 19:00 +0100
        Re: [PATCH] sched: idle: move need_resched check after function rcu_idle_enter Lianwei Wang <lianwei.wang@gmail.com> - 2015-11-23 21:10 +0100
  Re: [PATCH] sched: idle: move need_resched check after function  rcu_idle_enter Peter Zijlstra <peterz@infradead.org> - 2015-11-23 19:00 +0100

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