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From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <dsahern@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Mike Galbraith <efault@gmx.de>
Subject: Re: deadlock in scheduler enabling HRTICK feature
Date: Fri, 28 Jun 2013 11:18:53 +0200	[thread overview]
Message-ID: <20130628091853.GE29209@dyad.programming.kicks-ass.net> (raw)
In-Reply-To: <20130628090021.GA25431@gmail.com>

On Fri, Jun 28, 2013 at 11:00:21AM +0200, Ingo Molnar wrote:
> I guess we could merge this fix?

---
Subject: sched: Fix HRTICK

David reported that the HRTICK sched feature was borken; which was enough
motivation for me to finally fix it ;-)

We should not allow hrtimer code to do softirq wakeups while holding scheduler
locks. The hrtimer code only needs this when we accidentally try to program an
expired time. We don't much care about those anyway since we have the regular
tick to fall back to.

Reported-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9b1f2e5..0d8eb45 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -370,13 +370,6 @@ static struct rq *this_rq_lock(void)
 #ifdef CONFIG_SCHED_HRTICK
 /*
  * Use HR-timers to deliver accurate preemption points.
- *
- * Its all a bit involved since we cannot program an hrt while holding the
- * rq->lock. So what we do is store a state in in rq->hrtick_* and ask for a
- * reschedule event.
- *
- * When we get rescheduled we reprogram the hrtick_timer outside of the
- * rq->lock.
  */
 
 static void hrtick_clear(struct rq *rq)
@@ -404,6 +397,15 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
 }
 
 #ifdef CONFIG_SMP
+
+static int __hrtick_restart(struct rq *rq)
+{
+	struct hrtimer *timer = &rq->hrtick_timer;
+	ktime_t time = hrtimer_get_softexpires(timer);
+
+	return __hrtimer_start_range_ns(timer, time, 0, HRTIMER_MODE_ABS_PINNED, 0);
+}
+
 /*
  * called from hardirq (IPI) context
  */
@@ -412,7 +414,7 @@ static void __hrtick_start(void *arg)
 	struct rq *rq = arg;
 
 	raw_spin_lock(&rq->lock);
-	hrtimer_restart(&rq->hrtick_timer);
+	__hrtick_restart(rq);
 	rq->hrtick_csd_pending = 0;
 	raw_spin_unlock(&rq->lock);
 }
@@ -430,7 +432,7 @@ void hrtick_start(struct rq *rq, u64 delay)
 	hrtimer_set_expires(timer, time);
 
 	if (rq == this_rq()) {
-		hrtimer_restart(timer);
+		__hrtick_restart(rq);
 	} else if (!rq->hrtick_csd_pending) {
 		__smp_call_function_single(cpu_of(rq), &rq->hrtick_csd, 0);
 		rq->hrtick_csd_pending = 1;


  reply	other threads:[~2013-06-28  9:19 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-06-25 21:05 David Ahern
2013-06-25 21:17 ` Peter Zijlstra
2013-06-25 21:20   ` David Ahern
2013-06-26  7:05     ` Peter Zijlstra
2013-06-26 16:46       ` David Ahern
2013-06-27 10:43         ` Peter Zijlstra
2013-06-27 10:53           ` Peter Zijlstra
2013-06-27 12:28             ` Mike Galbraith
2013-06-27 13:06             ` Ingo Molnar
2013-06-27 19:18             ` Andy Lutomirski
2013-06-27 20:37               ` Peter Zijlstra
2013-06-27 22:28           ` David Ahern
2013-06-28  9:00             ` Ingo Molnar
2013-06-28  9:18               ` Peter Zijlstra [this message]
2013-07-12 13:29                 ` [tip:sched/core] sched: Fix HRTICK tip-bot for Peter Zijlstra
2013-06-28  9:09             ` deadlock in scheduler enabling HRTICK feature Peter Zijlstra
2013-06-28 17:28               ` David Ahern

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