linux-kernel - Re: [PATCH v2] sched: rt_rq runtime leakage bug fix

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Message-ID: <20110515083318.GJ2258@linux.vnet.ibm.com>
Date:	Sun, 15 May 2011 01:33:18 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Cheng Xu <chengxu@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sched: rt_rq runtime leakage bug fix

On Sat, May 14, 2011 at 02:20:02PM +0800, Cheng Xu wrote:
> 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>

Works for me!

Tested-by: Paul E. McKenney <paulmck@...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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