sched: for_each_domain() vs RCU

for_each_domain() uses RCU to serialize the sched_domains, except
it doesn't actually use rcu_read_lock() and instead relies on
disabling preemption -> FAIL.

XXX: audit other sched_domain code.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index eaa00014b499..43dc6d1d9e88 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1331,6 +1331,7 @@ static int select_task_rq_fair(struct task_struct *p, int flag, int sync)
                 new_cpu = prev_cpu;
         }
 
+        rcu_read_lock();
         for_each_domain(cpu, tmp) {
                 /*
                  * If power savings logic is enabled for a domain, see if we
@@ -1369,8 +1370,10 @@ static int select_task_rq_fair(struct task_struct *p, int flag, int sync)
                 if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
                     cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
 
-                        if (wake_affine(tmp, p, sync))
-                                return cpu;
+                        if (wake_affine(tmp, p, sync)) {
+                                new_cpu = cpu;
+                                goto out;
+                        }
 
                         want_affine = 0;
                 }
@@ -1416,6 +1419,8 @@ static int select_task_rq_fair(struct task_struct *p, int flag, int sync)
                 /* while loop will break here if sd == NULL */
         }
 
+out:
+        rcu_read_unlock();
         return new_cpu;
 }
 #endif /* CONFIG_SMP */