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>

diff --git a/kernel/sched.c b/kernel/sched.c
index 0cfe031..27d3e73 100644 (file)
--- 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 */