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Subject[PATCH -tip v2] sched: more sched_domain iterations fix
Date
From: Xiaotian Feng <dfeng@redhat.com>

sched_domain iterations needs to be protected by rcu_read_lock() now,
this patch adds another two places which needs the rcu lock, which is
spotted by following suspicious rcu_dereference_check() usage warnings.

kernel/sched_rt.c:1244 invoked rcu_dereference_check() without protection!
kernel/sched_stats.h:41 invoked rcu_dereference_check() without protection!

Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
---
kernel/sched_rt.c | 10 ++++++++--
kernel/sched_stats.h | 4 ++--
2 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 19ecb31..46a9533 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1241,6 +1241,7 @@ static int find_lowest_rq(struct task_struct *task)
if (!cpumask_test_cpu(this_cpu, lowest_mask))
this_cpu = -1; /* Skip this_cpu opt if not among lowest */

+ rcu_read_lock();
for_each_domain(cpu, sd) {
if (sd->flags & SD_WAKE_AFFINE) {
int best_cpu;
@@ -1250,15 +1251,20 @@ static int find_lowest_rq(struct task_struct *task)
* remote processor.
*/
if (this_cpu != -1 &&
- cpumask_test_cpu(this_cpu, sched_domain_span(sd)))
+ cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
+ rcu_read_unlock();
return this_cpu;
+ }

best_cpu = cpumask_first_and(lowest_mask,
sched_domain_span(sd));
- if (best_cpu < nr_cpu_ids)
+ if (best_cpu < nr_cpu_ids) {
+ rcu_read_unlock();
return best_cpu;
+ }
}
}
+ rcu_read_unlock();

/*
* And finally, if there were no matches within the domains
diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index 48ddf43..331e01b 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -37,7 +37,7 @@ static int show_schedstat(struct seq_file *seq, void *v)

#ifdef CONFIG_SMP
/* domain-specific stats */
- preempt_disable();
+ rcu_read_lock();
for_each_domain(cpu, sd) {
enum cpu_idle_type itype;

@@ -64,7 +64,7 @@ static int show_schedstat(struct seq_file *seq, void *v)
sd->ttwu_wake_remote, sd->ttwu_move_affine,
sd->ttwu_move_balance);
}
- preempt_enable();
+ rcu_read_unlock();
#endif
}
kfree(mask_str);
--
1.7.1


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