sched: Fix sched_domain iterations vs. RCU

Vladis Kletnieks reported a new RCU debug warning in the scheduler.

Since commit dce840a08702b ("sched: Dynamically allocate sched_domain/
sched_group data-structures") the sched_domain trees are protected by
RCU instead of RCU-sched.

This means that we need to include rcu_read_lock() protection when we
iterate them since disabling preemption doesn't suffice anymore.

Reported-by: Valdis.Kletnieks@vt.edu
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1302882741.2388.241.camel@twins
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 0cfe0310ed5d..27d3e73a2af6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1208,11 +1208,17 @@ int get_nohz_timer_target(void)
         int i;
         struct sched_domain *sd;
 
+        rcu_read_lock();
         for_each_domain(cpu, sd) {
-                for_each_cpu(i, sched_domain_span(sd))
-                        if (!idle_cpu(i))
-                                return i;
+                for_each_cpu(i, sched_domain_span(sd)) {
+                        if (!idle_cpu(i)) {
+                                cpu = i;
+                                goto unlock;
+                        }
+                }
         }
+unlock:
+        rcu_read_unlock();
         return cpu;
 }
 /*
@@ -2415,12 +2421,14 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
                 struct sched_domain *sd;
 
                 schedstat_inc(p, se.statistics.nr_wakeups_remote);
+                rcu_read_lock();
                 for_each_domain(this_cpu, sd) {
                         if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
                                 schedstat_inc(sd, ttwu_wake_remote);
                                 break;
                         }
                 }
+                rcu_read_unlock();
         }
 #endif /* CONFIG_SMP */