sched, nohz: Change rq->nr_running to always use wrappers

Sometimes ->nr_running may cross 2 but interrupt is not being
sent to rq's cpu. In this case we don't reenable the timer.
Looks like this may be the reason for rare unexpected effects,
if nohz is enabled.

Patch replaces all places of direct changing of nr_running
and makes add_nr_running() caring about crossing border.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140508225830.2469.97461.stgit@localhost
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b2cbe81308af..600e2291a75c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1206,12 +1206,14 @@ extern void update_idle_cpu_load(struct rq *this_rq);
 
 extern void init_task_runnable_average(struct task_struct *p);
 
-static inline void inc_nr_running(struct rq *rq)
+static inline void add_nr_running(struct rq *rq, unsigned count)
 {
-        rq->nr_running++;
+        unsigned prev_nr = rq->nr_running;
+
+        rq->nr_running = prev_nr + count;
 
 #ifdef CONFIG_NO_HZ_FULL
-        if (rq->nr_running == 2) {
+        if (prev_nr < 2 && rq->nr_running >= 2) {
                 if (tick_nohz_full_cpu(rq->cpu)) {
                         /* Order rq->nr_running write against the IPI */
                         smp_wmb();
@@ -1221,9 +1223,9 @@ static inline void inc_nr_running(struct rq *rq)
 #endif
 }
 
-static inline void dec_nr_running(struct rq *rq)
+static inline void sub_nr_running(struct rq *rq, unsigned count)
 {
-        rq->nr_running--;
+        rq->nr_running -= count;
 }
 
 static inline void rq_last_tick_reset(struct rq *rq)