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Date: Sat, 14 May 2011 14:20:02 +0800
From: Cheng Xu <chengxu@...ux.vnet.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: Ingo Molnar <mingo@...e.hu>,
Paul Mckenney <paulmck@...ux.vnet.ibm.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] sched: rt_rq runtime leakage bug fix
This patch is to fix the real-time scheduler bug reported at
https://lkml.org/lkml/2011/4/26/13. That is, when running multiple real-time
threads on every logical CPUs and then turning off one CPU, the kernel will
bug at function __disable_runtime().
Function __disable_runtime() bugs and reports leakage of rt_rq runtime. The
root cause is __disable_runtime() assumes it iterates through all the existing
rt_rq's while walking rq->leaf_rt_rq_list, which actually contains only
runnable rt_rq's. This problem also applies to __enable_runtime() and
print_rt_stats().
The patch is based on above analysis, appears to fix the problem, but is only
lightly tested.
Reported-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Cheng Xu <chengxu@...ux.vnet.ibm.com>
---
kernel/sched_rt.c | 22 +++++++++++++++++++---
1 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index e7cebdc..f8fcf82 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -183,6 +183,14 @@ static inline u64 sched_rt_period(struct rt_rq *rt_rq)
return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
}
+typedef struct task_group *rt_rq_iter_t;
+
+#define for_each_rt_rq(rt_rq, iter, rq) \
+ for (iter = list_entry_rcu(task_groups.next, typeof(*iter), list); \
+ (&iter->list != &task_groups) && \
+ (rt_rq = iter->rt_rq[cpu_of(rq)]); \
+ iter = list_entry_rcu(iter->list.next, typeof(*iter), list))
+
static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
{
list_add_rcu(&rt_rq->leaf_rt_rq_list,
@@ -288,6 +296,11 @@ static inline u64 sched_rt_period(struct rt_rq *rt_rq)
return ktime_to_ns(def_rt_bandwidth.rt_period);
}
+typedef struct rt_rq *rt_rq_iter_t;
+
+#define for_each_rt_rq(rt_rq, iter, rq) \
+ for ((void) iter, rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
+
static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
{
}
@@ -402,12 +415,13 @@ next:
static void __disable_runtime(struct rq *rq)
{
struct root_domain *rd = rq->rd;
+ rt_rq_iter_t iter;
struct rt_rq *rt_rq;
if (unlikely(!scheduler_running))
return;
- for_each_leaf_rt_rq(rt_rq, rq) {
+ for_each_rt_rq(rt_rq, iter, rq) {
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
s64 want;
int i;
@@ -487,6 +501,7 @@ static void disable_runtime(struct rq *rq)
static void __enable_runtime(struct rq *rq)
{
+ rt_rq_iter_t iter;
struct rt_rq *rt_rq;
if (unlikely(!scheduler_running))
@@ -495,7 +510,7 @@ static void __enable_runtime(struct rq *rq)
/*
* Reset each runqueue's bandwidth settings
*/
- for_each_leaf_rt_rq(rt_rq, rq) {
+ for_each_rt_rq(rt_rq, iter, rq) {
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
raw_spin_lock(&rt_b->rt_runtime_lock);
@@ -1796,10 +1811,11 @@ extern void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq);
static void print_rt_stats(struct seq_file *m, int cpu)
{
+ rt_rq_iter_t iter;
struct rt_rq *rt_rq;
rcu_read_lock();
- for_each_leaf_rt_rq(rt_rq, cpu_rq(cpu))
+ for_each_rt_rq(rt_rq, iter, cpu_rq(cpu))
print_rt_rq(m, cpu, rt_rq);
rcu_read_unlock();
}
--
1.7.1
--
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