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Subject[tip:sched/core] sched: Fix sched_domain iterations vs. RCU
Commit-ID:  057f3fadb347e9c51b07e1b277bbdda79f976768
Gitweb: http://git.kernel.org/tip/057f3fadb347e9c51b07e1b277bbdda79f976768
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Mon, 18 Apr 2011 11:24:34 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 19 Apr 2011 10:56:54 +0200

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>
---
kernel/sched.c | 14 +++++++++++---
1 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 0cfe031..27d3e73 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 */


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