linux-kernel - Re: [PATCH] sched/deadline: overrun could happen in start_hrtick

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Message-ID: <20140708093334.GD6758@twins.programming.kicks-ass.net>
Date:	Tue, 8 Jul 2014 11:33:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"xiaofeng.yan" <xiaofeng.yan@...wei.com>
Cc:	mingo@...hat.com, juri.lelli@...il.com,
	linux-kernel@...r.kernel.org, xiaofeng.yan2012@...il.com
Subject: Re: [PATCH] sched/deadline: overrun could happen in start_hrtick_dl

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.

---
 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);
+	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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