[tip:sched/core] sched: for_each_domain() vs RCU

tip-bot for Peter Zijlstra
2009-09-16T10:21:48Z

Commit-ID: 83f54960c11a14942ab00b54c51e91906b9d8235
Gitweb: http://git.kernel.org/tip/83f54960c11a14942ab00b54c51e91906b9d8235
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Thu, 10 Sep 2009 18:18:47 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 15 Sep 2009 16:01:06 +0200

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>

---
kernel/sched_fair.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index eaa0001..43dc6d1 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 */