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>

diff --git a/kernel/sched.c b/kernel/sched.c
index 8a1257b655609e850d67897c83dca6d367d10bdf..90329f1f8941762e99e89a5dac135ffce735f2d7 100644 (file)
--- 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)) {