Commit ec514c48 authored by Cheng Xu's avatar Cheng Xu Committed by Ingo Molnar
Browse files

sched: Fix rt_rq runtime leakage bug 

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarCheng Xu <chengxu@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4DCE1F12.6040609@linux.vnet.ibm.com


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent bd1a643e

kernel/sched_rt.c

+19 −3
Original line number Diff line number Diff line
@@ -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();

}

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