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Date: Thu, 12 May 2011 01:30:02 +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: Re: [PATCH] sched: rt_rq runtime leakage bug fix
Hi Peter,
I tried but hit a boot-time error "Unable to handle kernel paging request for data at address 0x100000008", and therefore would like to propose an alternative patch like,
#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))
This worked, it seems to pass the tests. Is this correct from a scheduler perspective?
For the not CONFIG_RT_GROUP_SCHED part, I used
typedef struct rt_rq *rt_rq_iter_t;
#define for_each_rt_rq(rt_rq, iter, rq) \
(void) iter; \
for (rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
An alternative is
#define for_each_rt_rq(rt_rq, iter, rq) \
for (rt_rq = iter = &rq->rt; iter; rt_rq = iter = NULL)
The patch is attached below. Could you check whether it is workable? Thank you.
---
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..f9e621a 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -183,6 +183,13 @@ 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 +295,12 @@ 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) \
+ (void) iter; \
+ for (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
On 2011-5-11 17:21, Peter Zijlstra wrote:
> On Wed, 2011-05-11 at 15:34 +0800, Cheng Xu wrote:
>> This patch is to fix bug report https://lkml.org/lkml/2011/4/26/13
>
> This really doesn't tell me anything, please restate the relevant
> information.
>
>> Function __disable_runtime() 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().
>
> Teach your mailer to wrap at 78 characters for changelogs.
>
>> The patch is based on above analysis, appears to fix the problem, but is only lightly tested.
>>
>>
>> Signed-off-by: Cheng Xu <chengxu@...ux.vnet.ibm.com>
>> Tested-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>>
>
> Don't leave whitespace between the tags and the tripple-dash. Also, I'm
> suspecting you're missing a Reported-by: paulmck tag.
>
>> ---
>> kernel/sched_rt.c | 31 ++++++++++++++++++++++++-------
>> 1 files changed, 24 insertions(+), 7 deletions(-)
>>
>> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
>> index e7cebdc..7f478ff 100644
>> --- a/kernel/sched_rt.c
>> +++ b/kernel/sched_rt.c
>> @@ -183,6 +183,13 @@ static inline u64 sched_rt_period(struct rt_rq *rt_rq)
>> return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
>> }
>>
>> +#define rt_rq_of_rq_decls(name) struct task_group *name
>> +
>> +#define list_for_rt_rq_of_rq(iterator, rq) \
>> + list_for_each_entry_rcu(iterator, &task_groups, list)
>> +
>> +#define rt_rq_of_rq_deref(iterator, rq) (iterator->rt_rq[cpu_of(rq)])
>> +
>> static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
>> {
>> list_add_rcu(&rt_rq->leaf_rt_rq_list,
>> @@ -288,6 +295,13 @@ static inline u64 sched_rt_period(struct rt_rq *rt_rq)
>> return ktime_to_ns(def_rt_bandwidth.rt_period);
>> }
>>
>> +#define rt_rq_of_rq_decls(name) struct rt_rq *name
>> +
>> +#define list_for_rt_rq_of_rq(iterator, rq) \
>> + for (iterator = &rq->rt; iterator; iterator = NULL)
>> +
>> +#define rt_rq_of_rq_deref(iterator, rq) (iterator)
>> +
>> static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
>> {
>> }
>
> So I see why you did that, I just don't much like it.. esp the decls
> macros, C has typedef to deal with that problem, also you can get rid of
> the deref macros (now if we were allowed C99 we could avoid the whole
> iter thing and declare a for-scope variable).
>
> How about something like:
>
> 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), \
> rt_rq = iter->rt_rq[cpu_of(rq)]; &iter->list != &task_groups; \
> iter = list_entry_rcu(iter->list.next, typeof(*iter), list), \
> rt_rq = iter->rt_rq[cpu_of(rq)])
>
>
> which is then used like:
>
> rt_rq_iter_t iter;
> struct rt_rq *rt_rq;
>
> for_each_rt_rq(rt_rq, iter, rq) {
> /* do something with rt_rq */
> }
>
>
--
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