Re: [PATCH] sched/deadline: overrun could happen in start_hrtick_dl

["xiaofeng.yan" <xiaofeng.yan@huawei.com>]

On 2014/7/8 19:23, xiaofeng.yan wrote:
> On 2014/7/8 17:33, Peter Zijlstra wrote:
>> On Tue, Jul 08, 2014 at 08:53:27AM +0000, xiaofeng.yan wrote:
>>>   static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
>>>   {
>>> -    s64 delta = p->dl.dl_runtime - p->dl.runtime;
>>> -
>>> -    if (delta > 10000)
>>> -        hrtick_start(rq, p->dl.runtime);
>>> +    delta = max_t(s64, 10000LL, delta);
>>> +    hrtick_start(rq, delta);
>>>   }
>> no, no, no. I said to unify the test.
>
> I understand your idea after reading the next patch. This is good 
> solution.
> I will test it with your patch.
>

I have tested this solution, It can work very well with deadline 
schedule class.

  kernel/sched/core.c     |    9 ++++++++-
  kernel/sched/deadline.c |    5 +----
  kernel/sched/fair.c     |    8 --------
  3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3bdf01b..cc9a058 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -442,8 +442,15 @@ static void __hrtick_start(void *arg)
  void hrtick_start(struct rq *rq, u64 delay)
  {
         struct hrtimer *timer = &rq->hrtick_timer;
-       ktime_t time = ktime_add_ns(timer->base->get_time(), delay);

+       ktime_t time;
+
+       /*
+        * Don't schedule slices shorter than 10000ns, that just
+        * doesn't make sense and can cause timer DoS.
+        */
+       s64 delta = max_t(s64, delay, 10000LL);
+       time = ktime_add_ns(timer->base->get_time(), delta);
         hrtimer_set_expires(timer, time);

         if (rq == this_rq()) {
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fc4f98b1..9135771 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -997,10 +997,7 @@ static void check_preempt_curr_dl(struct rq *rq, 
struct task_struct *p,
  #ifdef CONFIG_SCHED_HRTICK
static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
  {
-       s64 delta = p->dl.dl_runtime - p->dl.runtime;
-
-       if (delta > 10000)
-               hrtick_start(rq, p->dl.runtime);
+       hrtick_start(rq, p->dl.runtime);
  }
  #endif

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fea7d33..e5cfd57 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3857,14 +3857,6 @@ static void hrtick_start_fair(struct rq *rq, 
struct task_struct *p)
                                 resched_task(p);
                         return;
                 }
-
-               /*
-                * Don't schedule slices shorter than 10000ns, that just
-                * doesn't make sense. Rely on vruntime for fairness.
-                */
-               if (rq->curr != p)
-                       delta = max_t(s64, 10000LL, delta);
-
                 hrtick_start(rq, delta);
         }
  }
-- 


>> ---
>>   kernel/sched/core.c     | 9 ++++++++-
>>   kernel/sched/deadline.c | 3 +--
>>   kernel/sched/fair.c     | 7 -------
>>   3 files changed, 9 insertions(+), 10 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index e1a2f31bb0cb..c7b8a6fbac66 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -444,7 +444,14 @@ static void __hrtick_start(void *arg)
>>   void hrtick_start(struct rq *rq, u64 delay)
>>   {
>>       struct hrtimer *timer = &rq->hrtick_timer;
>> -    ktime_t time = ktime_add_ns(timer->base->get_time(), delay);
>> +    ktime_t time;
>> +
>> +    /*
>> +     * Don't schedule slices shorter than 10000ns, that just
>> +     * doesn't make sense and can cause timer DoS.
>> +     */
>> +    delta = max_t(s64, delta, 10000LL);
>
> transfer the argument delta to delay
>
>> +    time = ktime_add_ns(timer->base->get_time(), delay);
>>         hrtimer_set_expires(timer, time);
>>   diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index fc4f98b1258f..e1e24eea8061 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -999,8 +999,7 @@ static void start_hrtick_dl(struct rq *rq, struct 
>> task_struct *p)
>>   {
>>       s64 delta = p->dl.dl_runtime - p->dl.runtime;
>>   -    if (delta > 10000)
>> -        hrtick_start(rq, p->dl.runtime);
>> +    hrtick_start(rq, p->dl.runtime);
>>   }
>>   #endif
>>   diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 923fe32db6b3..713c58d2a7b0 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3901,13 +3901,6 @@ static void hrtick_start_fair(struct rq *rq, 
>> struct task_struct *p)
>>               return;
>>           }
>>   -        /*
>> -         * Don't schedule slices shorter than 10000ns, that just
>> -         * doesn't make sense. Rely on vruntime for fairness.
>> -         */
>> -        if (rq->curr != p)
>> -            delta = max_t(s64, 10000LL, delta);
>> -
>>           hrtick_start(rq, delta);
>>       }
>>   }
>
>
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