sched: check for SD_SERIALIZE atomically in rebalance_domains()

Nothing really serious here, mainly just a matter of nit-picking :-/

From: Dmitry Adamushko <dmitry.adamushko@gmail.com>
For CONFIG_SCHED_DEBUG && CONFIG_SYSCT configs, sd->flags can be altered
while being manipulated in rebalance_domains(). Let's do an atomic check.
We rely here on the atomicity of read/write accesses for aligned words.

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 8a1257b65560..90329f1f8941 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3668,6 +3668,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
         /* Earliest time when we have to do rebalance again */
         unsigned long next_balance = jiffies + 60*HZ;
         int update_next_balance = 0;
+        int need_serialize;
         cpumask_t tmp;
 
         for_each_domain(cpu, sd) {
@@ -3685,8 +3686,9 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
                 if (interval > HZ*NR_CPUS/10)
                         interval = HZ*NR_CPUS/10;
 
+                need_serialize = sd->flags & SD_SERIALIZE;
 
-                if (sd->flags & SD_SERIALIZE) {
+                if (need_serialize) {
                         if (!spin_trylock(&balancing))
                                 goto out;
                 }
@@ -3702,7 +3704,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
                         }
                         sd->last_balance = jiffies;
                 }
-                if (sd->flags & SD_SERIALIZE)
+                if (need_serialize)
                         spin_unlock(&balancing);
 out:
                 if (time_after(next_balance, sd->last_balance + interval)) {